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 $41.54   3.798%   $43.1177   $43.12   $43.10   $43.10  
  Purchase #2 $224.86   5.188%   $236.5257   $236.53   $236.55   $236.50  
  Purchase #3 $83.56   3.518%   $86.4996   $86.50   $86.50   $86.50  
  Purchase #4 $158.50   7.147%   $169.828   $169.83   $169.85   $169.80  
  Purchase #5 $176.46   7.585%   $189.8445   $189.84   $189.85   $189.80  
  Purchase #6 $82.90   12.331%   $93.1224   $93.12   $93.10   $93.10  
  Purchase #7 $116.85   13.126%   $132.1877   $132.19   $132.20   $132.20  
  7 purchase totals = $884.67       $951.1256   $951.13   $951.15   $951.00