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 $85.92   11.828%   $96.0826   $96.08   $96.10   $96.10  
  Purchase #2 $26.26   5.677%   $27.7508   $27.75   $27.75   $27.80  
  Purchase #3 $225.38   4.675%   $235.9165   $235.92   $235.90   $235.90  
  Purchase #4 $190.95   6.867%   $204.0625   $204.06   $204.05   $204.10  
  Purchase #5 $217.93   13.790%   $247.9825   $247.98   $248.00   $248.00  
  Purchase #6 $249.63   4.322%   $260.419   $260.42   $260.40   $260.40  
  Purchase #7 $151.93   12.692%   $171.213   $171.21   $171.20   $171.20  
  7 purchase totals = $1,148.00       $1,243.4269   $1,243.42   $1,243.40   $1,243.50