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 $66.61   13.665%   $75.7123   $75.71   $75.70   $75.70  
  Purchase #2 $248.35   9.685%   $272.4027   $272.40   $272.40   $272.40  
  Purchase #3 $174.96   4.536%   $182.8962   $182.90   $182.90   $182.90  
  Purchase #4 $25.54   13.443%   $28.9733   $28.97   $28.95   $29.00  
  Purchase #5 $211.73   10.753%   $234.4973   $234.50   $234.50   $234.50  
  Purchase #6 $46.89   4.463%   $48.9827   $48.98   $49.00   $49.00  
  Purchase #7 $189.70   8.812%   $206.4164   $206.42   $206.40   $206.40  
  7 purchase totals = $963.78       $1,049.8809   $1,049.88   $1,049.85   $1,049.90