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 $225.71   5.761%   $238.7132   $238.71   $238.70   $238.70  
  Purchase #2 $66.51   13.103%   $75.2248   $75.22   $75.20   $75.20  
  Purchase #3 $41.96   9.620%   $45.9966   $46.00   $46.00   $46.00  
  Purchase #4 $222.73   13.232%   $252.2016   $252.20   $252.20   $252.20  
  Purchase #5 $208.43   13.359%   $236.2742   $236.27   $236.25   $236.30  
  Purchase #6 $112.29   6.435%   $119.5159   $119.52   $119.50   $119.50  
  Purchase #7 $60.98   12.182%   $68.4086   $68.41   $68.40   $68.40  
  7 purchase totals = $938.61       $1,036.3349   $1,036.33   $1,036.25   $1,036.30