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 $249.35   5.382%   $262.77   $262.77   $262.75   $262.80  
  Purchase #2 $106.74   12.645%   $120.2373   $120.24   $120.25   $120.20  
  Purchase #3 $41.37   11.662%   $46.1946   $46.19   $46.20   $46.20  
  Purchase #4 $217.56   12.160%   $244.0153   $244.02   $244.00   $244.00  
  Purchase #5 $13.67   6.730%   $14.59   $14.59   $14.60   $14.60  
  Purchase #6 $51.90   5.142%   $54.5687   $54.57   $54.55   $54.60  
  Purchase #7 $213.89   8.414%   $231.8867   $231.89   $231.90   $231.90  
  7 purchase totals = $894.48       $974.2626   $974.27   $974.25   $974.30