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 $226.73   7.173%   $242.9933   $242.99   $243.00   $243.00  
  Purchase #2 $173.42   5.354%   $182.7049   $182.70   $182.70   $182.70  
  Purchase #3 $39.52   11.424%   $44.0348   $44.03   $44.05   $44.00  
  Purchase #4 $43.48   8.476%   $47.1654   $47.17   $47.15   $47.20  
  Purchase #5 $87.55   13.213%   $99.118   $99.12   $99.10   $99.10  
  Purchase #6 $247.55   9.536%   $271.1564   $271.16   $271.15   $271.20  
  Purchase #7 $135.69   7.782%   $146.2494   $146.25   $146.25   $146.20  
  7 purchase totals = $953.94       $1,033.4222   $1,033.42   $1,033.40   $1,033.40