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 $205.96   13.571%   $233.9108   $233.91   $233.90   $233.90  
  Purchase #2 $117.66   12.851%   $132.7805   $132.78   $132.80   $132.80  
  Purchase #3 $85.83   7.796%   $92.5213   $92.52   $92.50   $92.50  
  Purchase #4 $207.98   12.824%   $234.6514   $234.65   $234.65   $234.70  
  Purchase #5 $221.43   9.671%   $242.8445   $242.84   $242.85   $242.80  
  Purchase #6 $218.39   5.850%   $231.1658   $231.17   $231.15   $231.20  
  Purchase #7 $118.83   12.756%   $133.988   $133.99   $134.00   $134.00  
  7 purchase totals = $1,176.08       $1,301.8623   $1,301.86   $1,301.85   $1,301.90