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 $248.42   10.687%   $274.9686   $274.97   $274.95   $275.00  
  Purchase #2 $194.84   6.580%   $207.6605   $207.66   $207.65   $207.70  
  Purchase #3 $210.76   12.736%   $237.6024   $237.60   $237.60   $237.60  
  Purchase #4 $92.44   5.217%   $97.2626   $97.26   $97.25   $97.30  
  Purchase #5 $92.52   5.409%   $97.5244   $97.52   $97.50   $97.50  
  Purchase #6 $14.55   4.558%   $15.2132   $15.21   $15.20   $15.20  
  Purchase #7 $204.29   7.545%   $219.7037   $219.70   $219.70   $219.70  
  7 purchase totals = $1,057.82       $1,149.9354   $1,149.92   $1,149.85   $1,150.00