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 $7.74   6.582%   $8.2494   $8.25   $8.25   $8.20  
  Purchase #2 $167.87   12.824%   $189.3976   $189.40   $189.40   $189.40  
  Purchase #3 $25.56   6.658%   $27.2618   $27.26   $27.25   $27.30  
  Purchase #4 $236.99   7.814%   $255.5084   $255.51   $255.50   $255.50  
  Purchase #5 $85.75   11.132%   $95.2957   $95.30   $95.30   $95.30  
  Purchase #6 $214.60   9.251%   $234.4526   $234.45   $234.45   $234.50  
  Purchase #7 $216.63   12.828%   $244.4193   $244.42   $244.40   $244.40  
  7 purchase totals = $955.14       $1,054.5848   $1,054.59   $1,054.55   $1,054.60