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 $213.93   9.176%   $233.5602   $233.56   $233.55   $233.60  
  Purchase #2 $177.80   12.290%   $199.6516   $199.65   $199.65   $199.70  
  Purchase #3 $94.88   4.522%   $99.1705   $99.17   $99.15   $99.20  
  Purchase #4 $187.75   9.471%   $205.5318   $205.53   $205.55   $205.50  
  Purchase #5 $29.43   9.378%   $32.1899   $32.19   $32.20   $32.20  
  Purchase #6 $164.97   6.578%   $175.8217   $175.82   $175.80   $175.80  
  Purchase #7 $89.43   4.419%   $93.3819   $93.38   $93.40   $93.40  
  7 purchase totals = $958.19       $1,039.3076   $1,039.30   $1,039.30   $1,039.40