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 $236.73   12.708%   $266.8136   $266.81   $266.80   $266.80  
  Purchase #2 $53.27   8.639%   $57.872   $57.87   $57.85   $57.90  
  Purchase #3 $219.32   9.283%   $239.6795   $239.68   $239.70   $239.70  
  Purchase #4 $189.33   5.500%   $199.7432   $199.74   $199.75   $199.70  
  Purchase #5 $216.25   11.426%   $240.9587   $240.96   $240.95   $241.00  
  Purchase #6 $217.85   13.370%   $246.9765   $246.98   $247.00   $247.00  
  Purchase #7 $202.37   11.801%   $226.2517   $226.25   $226.25   $226.30  
  7 purchase totals = $1,335.12       $1,478.2952   $1,478.29   $1,478.30   $1,478.40