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 $182.63   6.114%   $193.796   $193.80   $193.80   $193.80  
  Purchase #2 $101.95   7.156%   $109.2455   $109.25   $109.25   $109.20  
  Purchase #3 $76.86   13.653%   $87.3537   $87.35   $87.35   $87.40  
  Purchase #4 $24.71   4.664%   $25.8625   $25.86   $25.85   $25.90  
  Purchase #5 $166.40   5.256%   $175.146   $175.15   $175.15   $175.10  
  Purchase #6 $45.56   7.572%   $49.0098   $49.01   $49.00   $49.00  
  Purchase #7 $215.92   12.699%   $243.3397   $243.34   $243.35   $243.30  
  7 purchase totals = $814.03       $883.7532   $883.76   $883.75   $883.70