Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $229.50   13.138%   $259.6517   $259.65   $259.65   $259.70  
  Purchase #2 $136.72   7.759%   $147.3281   $147.33   $147.35   $147.30  
  Purchase #3 $130.31   3.286%   $134.592   $134.59   $134.60   $134.60  
  Purchase #4 $114.93   11.309%   $127.9274   $127.93   $127.95   $127.90  
  Purchase #5 $170.38   3.363%   $176.1099   $176.11   $176.10   $176.10  
  Purchase #6 $194.56   4.288%   $202.9027   $202.90   $202.90   $202.90  
  Purchase #7 $138.91   10.813%   $153.9303   $153.93   $153.95   $153.90  
  7 purchase totals = $1,115.31       $1,202.4421   $1,202.44   $1,202.50   $1,202.40