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 $67.63   9.143%   $73.8134   $73.81   $73.80   $73.80  
  Purchase #2 $162.93   8.253%   $176.3766   $176.38   $176.40   $176.40  
  Purchase #3 $250.60   12.803%   $282.6843   $282.68   $282.70   $282.70  
  Purchase #4 $190.33   12.243%   $213.6321   $213.63   $213.65   $213.60  
  Purchase #5 $17.71   12.492%   $19.9223   $19.92   $19.90   $19.90  
  Purchase #6 $177.35   11.341%   $197.4633   $197.46   $197.45   $197.50  
  Purchase #7 $109.89   10.114%   $121.0043   $121.00   $121.00   $121.00  
  7 purchase totals = $976.44       $1,084.8963   $1,084.88   $1,084.90   $1,084.90