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 $180.85   11.722%   $202.0492   $202.05   $202.05   $202.00  
  Purchase #2 $241.44   9.793%   $265.0842   $265.08   $265.10   $265.10  
  Purchase #3 $233.27   6.706%   $248.9131   $248.91   $248.90   $248.90  
  Purchase #4 $114.25   10.190%   $125.8921   $125.89   $125.90   $125.90  
  Purchase #5 $65.99   4.467%   $68.9378   $68.94   $68.95   $68.90  
  Purchase #6 $123.83   3.375%   $128.0093   $128.01   $128.00   $128.00  
  Purchase #7 $235.34   11.349%   $262.0487   $262.05   $262.05   $262.00  
  7 purchase totals = $1,194.97       $1,300.9344   $1,300.93   $1,300.95   $1,300.80