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 $94.82   3.204%   $97.858   $97.86   $97.85   $97.90  
  Purchase #2 $144.26   6.428%   $153.533   $153.53   $153.55   $153.50  
  Purchase #3 $156.48   3.408%   $161.8128   $161.81   $161.80   $161.80  
  Purchase #4 $118.42   13.411%   $134.3013   $134.30   $134.30   $134.30  
  Purchase #5 $180.27   4.255%   $187.9405   $187.94   $187.95   $187.90  
  Purchase #6 $89.39   5.683%   $94.47   $94.47   $94.45   $94.50  
  Purchase #7 $53.74   10.181%   $59.2113   $59.21   $59.20   $59.20  
  7 purchase totals = $837.38       $889.1269   $889.12   $889.10   $889.10