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 $44.37   13.232%   $50.241   $50.24   $50.25   $50.20  
  Purchase #2 $28.81   13.545%   $32.7123   $32.71   $32.70   $32.70  
  Purchase #3 $41.43   8.447%   $44.9296   $44.93   $44.95   $44.90  
  Purchase #4 $32.87   12.407%   $36.9482   $36.95   $36.95   $36.90  
  Purchase #5 $212.72   3.398%   $219.9482   $219.95   $219.95   $219.90  
  Purchase #6 $237.97   12.432%   $267.5544   $267.55   $267.55   $267.60  
  Purchase #7 $128.78   4.853%   $135.0297   $135.03   $135.05   $135.00  
  7 purchase totals = $726.95       $787.3634   $787.36   $787.40   $787.20