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 $70.71   7.427%   $75.9616   $75.96   $75.95   $76.00  
  Purchase #2 $188.65   8.431%   $204.5551   $204.56   $204.55   $204.60  
  Purchase #3 $120.76   7.586%   $129.9209   $129.92   $129.90   $129.90  
  Purchase #4 $181.79   13.543%   $206.4098   $206.41   $206.40   $206.40  
  Purchase #5 $65.52   11.337%   $72.948   $72.95   $72.95   $72.90  
  Purchase #6 $172.98   6.796%   $184.7357   $184.74   $184.75   $184.70  
  Purchase #7 $229.69   13.680%   $261.1116   $261.11   $261.10   $261.10  
  7 purchase totals = $1,030.10       $1,135.6427   $1,135.65   $1,135.60   $1,135.60