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 $136.57   8.572%   $148.2768   $148.28   $148.30   $148.30  
  Purchase #2 $56.51   11.123%   $62.7956   $62.80   $62.80   $62.80  
  Purchase #3 $14.63   12.421%   $16.4472   $16.45   $16.45   $16.40  
  Purchase #4 $42.43   7.531%   $45.6254   $45.63   $45.65   $45.60  
  Purchase #5 $226.31   10.770%   $250.6836   $250.68   $250.70   $250.70  
  Purchase #6 $14.81   5.577%   $15.636   $15.64   $15.65   $15.60  
  Purchase #7 $200.85   4.299%   $209.4845   $209.48   $209.50   $209.50  
  7 purchase totals = $692.11       $748.9491   $748.96   $749.05   $748.90