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 $227.45   7.639%   $244.8249   $244.82   $244.80   $244.80  
  Purchase #2 $166.69   3.541%   $172.5925   $172.59   $172.60   $172.60  
  Purchase #3 $24.53   3.341%   $25.3495   $25.35   $25.35   $25.30  
  Purchase #4 $150.37   5.771%   $159.0479   $159.05   $159.05   $159.00  
  Purchase #5 $201.63   7.225%   $216.1978   $216.20   $216.20   $216.20  
  Purchase #6 $89.80   8.503%   $97.4357   $97.44   $97.45   $97.40  
  Purchase #7 $52.70   13.797%   $59.971   $59.97   $59.95   $60.00  
  7 purchase totals = $913.17       $975.4193   $975.42   $975.40   $975.30