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 $218.93   6.131%   $232.3526   $232.35   $232.35   $232.40  
  Purchase #2 $115.66   7.120%   $123.895   $123.90   $123.90   $123.90  
  Purchase #3 $212.63   13.634%   $241.62   $241.62   $241.60   $241.60  
  Purchase #4 $42.93   9.821%   $47.1462   $47.15   $47.15   $47.10  
  Purchase #5 $29.96   6.227%   $31.8256   $31.83   $31.85   $31.80  
  Purchase #6 $230.94   12.591%   $260.0177   $260.02   $260.00   $260.00  
  Purchase #7 $46.97   6.580%   $50.0606   $50.06   $50.05   $50.10  
  7 purchase totals = $898.02       $986.9177   $986.93   $986.90   $986.90