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 $57.33   6.155%   $60.8587   $60.86   $60.85   $60.90  
  Purchase #2 $53.37   11.598%   $59.5599   $59.56   $59.55   $59.60  
  Purchase #3 $117.80   5.208%   $123.935   $123.94   $123.95   $123.90  
  Purchase #4 $117.56   7.750%   $126.6709   $126.67   $126.65   $126.70  
  Purchase #5 $113.76   7.849%   $122.689   $122.69   $122.70   $122.70  
  Purchase #6 $176.85   12.771%   $199.4355   $199.44   $199.45   $199.40  
  Purchase #7 $103.90   8.864%   $113.1097   $113.11   $113.10   $113.10  
  7 purchase totals = $740.57       $806.2587   $806.27   $806.25   $806.30