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 $86.74   12.544%   $97.6207   $97.62   $97.60   $97.60  
  Purchase #2 $156.93   12.674%   $176.8193   $176.82   $176.80   $176.80  
  Purchase #3 $240.99   3.748%   $250.0223   $250.02   $250.00   $250.00  
  Purchase #4 $35.42   10.739%   $39.2238   $39.22   $39.20   $39.20  
  Purchase #5 $7.94   5.379%   $8.3671   $8.37   $8.35   $8.40  
  Purchase #6 $243.78   9.197%   $266.2004   $266.20   $266.20   $266.20  
  Purchase #7 $79.25   12.441%   $89.1095   $89.11   $89.10   $89.10  
  7 purchase totals = $851.05       $927.3631   $927.36   $927.25   $927.30