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 $207.96   12.354%   $233.6514   $233.65   $233.65   $233.70  
  Purchase #2 $73.29   13.638%   $83.2853   $83.29   $83.30   $83.30  
  Purchase #3 $234.90   3.861%   $243.9695   $243.97   $243.95   $244.00  
  Purchase #4 $142.58   11.171%   $158.5076   $158.51   $158.50   $158.50  
  Purchase #5 $236.38   13.279%   $267.7689   $267.77   $267.75   $267.80  
  Purchase #6 $233.52   9.209%   $255.0249   $255.02   $255.00   $255.00  
  Purchase #7 $50.26   3.738%   $52.1387   $52.14   $52.15   $52.10  
  7 purchase totals = $1,178.89       $1,294.3463   $1,294.35   $1,294.30   $1,294.40