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 $91.34   6.550%   $97.3228   $97.32   $97.30   $97.30  
  Purchase #2 $237.76   4.710%   $248.9585   $248.96   $248.95   $249.00  
  Purchase #3 $16.48   13.121%   $18.6423   $18.64   $18.65   $18.60  
  Purchase #4 $217.35   13.179%   $245.9946   $245.99   $246.00   $246.00  
  Purchase #5 $217.74   13.562%   $247.2699   $247.27   $247.25   $247.30  
  Purchase #6 $171.91   3.411%   $177.7739   $177.77   $177.75   $177.80  
  Purchase #7 $174.50   7.182%   $187.0326   $187.03   $187.05   $187.00  
  7 purchase totals = $1,127.08       $1,222.9946   $1,222.98   $1,222.95   $1,223.00