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 $78.57   12.299%   $88.2333   $88.23   $88.25   $88.20  
  Purchase #2 $169.87   4.365%   $177.2848   $177.28   $177.30   $177.30  
  Purchase #3 $63.75   7.554%   $68.5657   $68.57   $68.55   $68.60  
  Purchase #4 $248.58   7.623%   $267.5293   $267.53   $267.55   $267.50  
  Purchase #5 $46.57   3.681%   $48.2842   $48.28   $48.30   $48.30  
  Purchase #6 $205.90   3.590%   $213.2918   $213.29   $213.30   $213.30  
  Purchase #7 $217.87   13.716%   $247.753   $247.75   $247.75   $247.80  
  7 purchase totals = $1,031.11       $1,110.9421   $1,110.93   $1,111.00   $1,111.00