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 $32.70   5.767%   $34.5858   $34.59   $34.60   $34.60  
  Purchase #2 $95.68   9.651%   $104.9141   $104.91   $104.90   $104.90  
  Purchase #3 $240.71   13.619%   $273.4923   $273.49   $273.50   $273.50  
  Purchase #4 $231.82   13.576%   $263.2919   $263.29   $263.30   $263.30  
  Purchase #5 $166.31   6.363%   $176.8923   $176.89   $176.90   $176.90  
  Purchase #6 $151.33   7.688%   $162.9643   $162.96   $162.95   $163.00  
  Purchase #7 $244.42   11.297%   $272.0321   $272.03   $272.05   $272.00  
  7 purchase totals = $1,162.97       $1,288.1728   $1,288.16   $1,288.20   $1,288.20