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 $27.45   5.171%   $28.8694   $28.87   $28.85   $28.90  
  Purchase #2 $144.64   4.180%   $150.686   $150.69   $150.70   $150.70  
  Purchase #3 $42.90   12.870%   $48.4212   $48.42   $48.40   $48.40  
  Purchase #4 $137.65   13.419%   $156.1213   $156.12   $156.10   $156.10  
  Purchase #5 $56.90   5.560%   $60.0636   $60.06   $60.05   $60.10  
  Purchase #6 $247.82   10.125%   $272.9118   $272.91   $272.90   $272.90  
  Purchase #7 $84.72   3.579%   $87.7521   $87.75   $87.75   $87.80  
  7 purchase totals = $742.08       $804.8254   $804.82   $804.75   $804.90