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 $56.98   12.209%   $63.9367   $63.94   $63.95   $63.90  
  Purchase #2 $138.75   5.695%   $146.6518   $146.65   $146.65   $146.70  
  Purchase #3 $49.61   8.120%   $53.6383   $53.64   $53.65   $53.60  
  Purchase #4 $65.95   4.393%   $68.8472   $68.85   $68.85   $68.80  
  Purchase #5 $84.62   4.653%   $88.5574   $88.56   $88.55   $88.60  
  Purchase #6 $100.68   12.211%   $112.974   $112.97   $112.95   $113.00  
  Purchase #7 $230.40   8.692%   $250.4264   $250.43   $250.45   $250.40  
  7 purchase totals = $726.99       $785.0318   $785.04   $785.05   $785.00