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 $219.30   10.226%   $241.7256   $241.73   $241.75   $241.70  
  Purchase #2 $149.68   9.767%   $164.2992   $164.30   $164.30   $164.30  
  Purchase #3 $62.50   9.588%   $68.4925   $68.49   $68.50   $68.50  
  Purchase #4 $158.48   3.172%   $163.507   $163.51   $163.50   $163.50  
  Purchase #5 $75.41   12.726%   $85.0067   $85.01   $85.00   $85.00  
  Purchase #6 $168.66   5.806%   $178.4524   $178.45   $178.45   $178.50  
  Purchase #7 $141.30   5.332%   $148.8341   $148.83   $148.85   $148.80  
  7 purchase totals = $975.33       $1,050.3175   $1,050.32   $1,050.35   $1,050.30