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 $58.91   10.143%   $64.8852   $64.89   $64.90   $64.90  
  Purchase #2 $111.47   7.387%   $119.7043   $119.70   $119.70   $119.70  
  Purchase #3 $105.97   11.180%   $117.8174   $117.82   $117.80   $117.80  
  Purchase #4 $13.43   8.122%   $14.5208   $14.52   $14.50   $14.50  
  Purchase #5 $216.78   4.475%   $226.4809   $226.48   $226.50   $226.50  
  Purchase #6 $98.37   8.277%   $106.5121   $106.51   $106.50   $106.50  
  Purchase #7 $231.52   10.179%   $255.0864   $255.09   $255.10   $255.10  
  7 purchase totals = $836.45       $905.0071   $905.01   $905.00   $905.00