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 $190.83   9.242%   $208.4665   $208.47   $208.45   $208.50  
  Purchase #2 $60.56   12.857%   $68.3462   $68.35   $68.35   $68.30  
  Purchase #3 $240.81   8.199%   $260.554   $260.55   $260.55   $260.60  
  Purchase #4 $169.89   13.838%   $193.3994   $193.40   $193.40   $193.40  
  Purchase #5 $122.81   12.398%   $138.036   $138.04   $138.05   $138.00  
  Purchase #6 $243.64   9.505%   $266.798   $266.80   $266.80   $266.80  
  Purchase #7 $157.38   8.642%   $170.9808   $170.98   $171.00   $171.00  
  7 purchase totals = $1,185.92       $1,306.5809   $1,306.59   $1,306.60   $1,306.60