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 $97.42   7.374%   $104.6038   $104.60   $104.60   $104.60  
  Purchase #2 $93.88   5.413%   $98.9617   $98.96   $98.95   $99.00  
  Purchase #3 $24.41   4.800%   $25.5817   $25.58   $25.60   $25.60  
  Purchase #4 $92.49   13.647%   $105.1121   $105.11   $105.10   $105.10  
  Purchase #5 $238.82   8.532%   $259.1961   $259.20   $259.20   $259.20  
  Purchase #6 $232.69   13.813%   $264.8315   $264.83   $264.85   $264.80  
  Purchase #7 $41.41   7.584%   $44.5505   $44.55   $44.55   $44.60  
  7 purchase totals = $821.12       $902.8374   $902.83   $902.85   $902.90