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 $229.44   11.199%   $255.135   $255.14   $255.15   $255.10  
  Purchase #2 $239.36   7.259%   $256.7351   $256.74   $256.75   $256.70  
  Purchase #3 $41.54   6.438%   $44.2143   $44.21   $44.20   $44.20  
  Purchase #4 $188.64   11.695%   $210.7014   $210.70   $210.70   $210.70  
  Purchase #5 $102.45   13.183%   $115.956   $115.96   $115.95   $116.00  
  Purchase #6 $87.67   8.636%   $95.2412   $95.24   $95.25   $95.20  
  Purchase #7 $30.83   9.490%   $33.7558   $33.76   $33.75   $33.80  
  7 purchase totals = $919.93       $1,011.7388   $1,011.75   $1,011.75   $1,011.70