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 $30.93   11.546%   $34.5012   $34.50   $34.50   $34.50  
  Purchase #2 $100.95   10.200%   $111.2469   $111.25   $111.25   $111.20  
  Purchase #3 $93.41   12.114%   $104.7257   $104.73   $104.75   $104.70  
  Purchase #4 $20.54   11.158%   $22.8319   $22.83   $22.85   $22.80  
  Purchase #5 $60.37   9.791%   $66.2808   $66.28   $66.30   $66.30  
  Purchase #6 $228.28   13.167%   $258.3376   $258.34   $258.35   $258.30  
  Purchase #7 $133.26   11.215%   $148.2051   $148.21   $148.20   $148.20  
  7 purchase totals = $667.74       $746.1292   $746.14   $746.20   $746.00