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 $85.85   13.837%   $97.7291   $97.73   $97.75   $97.70  
  Purchase #2 $46.96   5.486%   $49.5362   $49.54   $49.55   $49.50  
  Purchase #3 $65.70   8.852%   $71.5158   $71.52   $71.50   $71.50  
  Purchase #4 $64.48   4.738%   $67.5351   $67.54   $67.55   $67.50  
  Purchase #5 $111.98   13.475%   $127.0693   $127.07   $127.05   $127.10  
  Purchase #6 $217.50   9.133%   $237.3643   $237.36   $237.35   $237.40  
  Purchase #7 $214.73   6.432%   $228.5414   $228.54   $228.55   $228.50  
  7 purchase totals = $807.20       $879.2912   $879.30   $879.30   $879.20