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 $78.67   11.238%   $87.5109   $87.51   $87.50   $87.50  
  Purchase #2 $244.98   9.663%   $268.6524   $268.65   $268.65   $268.70  
  Purchase #3 $225.37   13.303%   $255.351   $255.35   $255.35   $255.40  
  Purchase #4 $80.55   4.612%   $84.265   $84.27   $84.25   $84.30  
  Purchase #5 $14.84   7.673%   $15.9787   $15.98   $16.00   $16.00  
  Purchase #6 $193.74   7.335%   $207.9508   $207.95   $207.95   $208.00  
  Purchase #7 $190.36   4.687%   $199.2822   $199.28   $199.30   $199.30  
  7 purchase totals = $1,028.51       $1,118.9910   $1,118.99   $1,119.00   $1,119.20