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 $217.75   7.583%   $234.262   $234.26   $234.25   $234.30  
  Purchase #2 $106.93   8.165%   $115.6608   $115.66   $115.65   $115.70  
  Purchase #3 $158.34   10.397%   $174.8026   $174.80   $174.80   $174.80  
  Purchase #4 $30.87   7.477%   $33.1781   $33.18   $33.20   $33.20  
  Purchase #5 $108.97   7.686%   $117.3454   $117.35   $117.35   $117.30  
  Purchase #6 $39.68   4.496%   $41.464   $41.46   $41.45   $41.50  
  Purchase #7 $202.31   4.716%   $211.8509   $211.85   $211.85   $211.90  
  7 purchase totals = $864.85       $928.5638   $928.56   $928.55   $928.70