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 $23.86   7.530%   $25.6567   $25.66   $25.65   $25.70  
  Purchase #2 $82.36   13.357%   $93.3608   $93.36   $93.35   $93.40  
  Purchase #3 $96.81   9.216%   $105.732   $105.73   $105.75   $105.70  
  Purchase #4 $198.89   3.268%   $205.3897   $205.39   $205.40   $205.40  
  Purchase #5 $39.79   7.456%   $42.7567   $42.76   $42.75   $42.80  
  Purchase #6 $129.71   7.557%   $139.5122   $139.51   $139.50   $139.50  
  Purchase #7 $207.41   6.607%   $221.1136   $221.11   $221.10   $221.10  
  7 purchase totals = $778.83       $833.5217   $833.52   $833.50   $833.60