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 $145.61   11.564%   $162.4483   $162.45   $162.45   $162.40  
  Purchase #2 $162.47   6.130%   $172.4294   $172.43   $172.45   $172.40  
  Purchase #3 $150.48   10.143%   $165.7432   $165.74   $165.75   $165.70  
  Purchase #4 $202.92   5.172%   $213.415   $213.42   $213.40   $213.40  
  Purchase #5 $69.55   10.632%   $76.9446   $76.94   $76.95   $76.90  
  Purchase #6 $32.68   8.778%   $35.5487   $35.55   $35.55   $35.50  
  Purchase #7 $224.29   5.642%   $236.9444   $236.94   $236.95   $236.90  
  7 purchase totals = $988.00       $1,063.4736   $1,063.47   $1,063.50   $1,063.20