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 $242.47   7.295%   $260.1582   $260.16   $260.15   $260.20  
  Purchase #2 $172.95   10.560%   $191.2135   $191.21   $191.20   $191.20  
  Purchase #3 $184.52   3.773%   $191.4819   $191.48   $191.50   $191.50  
  Purchase #4 $198.51   13.692%   $225.69   $225.69   $225.70   $225.70  
  Purchase #5 $169.64   4.477%   $177.2348   $177.23   $177.25   $177.20  
  Purchase #6 $124.83   6.567%   $133.0276   $133.03   $133.05   $133.00  
  Purchase #7 $225.76   5.166%   $237.4228   $237.42   $237.40   $237.40  
  7 purchase totals = $1,318.68       $1,416.2288   $1,416.22   $1,416.25   $1,416.20