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 $246.59   5.451%   $260.0316   $260.03   $260.05   $260.00  
  Purchase #2 $75.29   8.718%   $81.8538   $81.85   $81.85   $81.90  
  Purchase #3 $125.93   10.331%   $138.9398   $138.94   $138.95   $138.90  
  Purchase #4 $110.80   5.399%   $116.7821   $116.78   $116.80   $116.80  
  Purchase #5 $76.39   9.153%   $83.382   $83.38   $83.40   $83.40  
  Purchase #6 $63.80   8.134%   $68.9895   $68.99   $69.00   $69.00  
  Purchase #7 $69.60   10.359%   $76.8099   $76.81   $76.80   $76.80  
  7 purchase totals = $768.40       $826.7887   $826.78   $826.85   $826.80