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 $134.26   12.662%   $151.26   $151.26   $151.25   $151.30  
  Purchase #2 $138.80   9.264%   $151.6584   $151.66   $151.65   $151.70  
  Purchase #3 $18.25   12.828%   $20.5911   $20.59   $20.60   $20.60  
  Purchase #4 $74.62   13.177%   $84.4527   $84.45   $84.45   $84.50  
  Purchase #5 $227.86   6.179%   $241.9395   $241.94   $241.95   $241.90  
  Purchase #6 $156.33   5.663%   $165.183   $165.18   $165.20   $165.20  
  Purchase #7 $162.90   11.797%   $182.1173   $182.12   $182.10   $182.10  
  7 purchase totals = $913.02       $997.2020   $997.20   $997.20   $997.30