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 $23.89   11.228%   $26.5724   $26.57   $26.55   $26.60  
  Purchase #2 $120.73   10.259%   $133.1157   $133.12   $133.10   $133.10  
  Purchase #3 $83.28   3.219%   $85.9608   $85.96   $85.95   $86.00  
  Purchase #4 $100.76   9.833%   $110.6677   $110.67   $110.65   $110.70  
  Purchase #5 $124.62   6.666%   $132.9272   $132.93   $132.95   $132.90  
  Purchase #6 $164.66   10.314%   $181.643   $181.64   $181.65   $181.60  
  Purchase #7 $237.51   11.165%   $264.028   $264.03   $264.05   $264.00  
  7 purchase totals = $855.45       $934.9148   $934.92   $934.90   $934.90