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 $138.82   10.722%   $153.7043   $153.70   $153.70   $153.70  
  Purchase #2 $92.69   3.554%   $95.9842   $95.98   $96.00   $96.00  
  Purchase #3 $235.27   6.431%   $250.4002   $250.40   $250.40   $250.40  
  Purchase #4 $95.71   12.305%   $107.4871   $107.49   $107.50   $107.50  
  Purchase #5 $184.30   13.111%   $208.4636   $208.46   $208.45   $208.50  
  Purchase #6 $147.26   13.172%   $166.6571   $166.66   $166.65   $166.70  
  Purchase #7 $57.44   7.403%   $61.6923   $61.69   $61.70   $61.70  
  7 purchase totals = $951.49       $1,044.3888   $1,044.38   $1,044.40   $1,044.50