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 $223.30   6.118%   $236.9615   $236.96   $236.95   $237.00  
  Purchase #2 $62.91   8.305%   $68.1347   $68.13   $68.15   $68.10  
  Purchase #3 $77.39   6.768%   $82.6278   $82.63   $82.65   $82.60  
  Purchase #4 $33.74   9.346%   $36.8933   $36.89   $36.90   $36.90  
  Purchase #5 $149.65   4.441%   $156.296   $156.30   $156.30   $156.30  
  Purchase #6 $210.69   10.363%   $232.5238   $232.52   $232.50   $232.50  
  Purchase #7 $152.63   6.655%   $162.7875   $162.79   $162.80   $162.80  
  7 purchase totals = $910.31       $976.2246   $976.22   $976.25   $976.20