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 $125.92   11.113%   $139.9135   $139.91   $139.90   $139.90  
  Purchase #2 $210.99   13.286%   $239.0221   $239.02   $239.00   $239.00  
  Purchase #3 $59.95   3.363%   $61.9661   $61.97   $61.95   $62.00  
  Purchase #4 $172.53   8.288%   $186.8293   $186.83   $186.85   $186.80  
  Purchase #5 $146.68   11.327%   $163.2944   $163.29   $163.30   $163.30  
  Purchase #6 $92.78   9.128%   $101.249   $101.25   $101.25   $101.20  
  Purchase #7 $55.96   3.658%   $58.007   $58.01   $58.00   $58.00  
  7 purchase totals = $864.81       $950.2814   $950.28   $950.25   $950.20