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 $75.44   9.665%   $82.7313   $82.73   $82.75   $82.70  
  Purchase #2 $248.83   8.692%   $270.4583   $270.46   $270.45   $270.50  
  Purchase #3 $160.77   6.706%   $171.5512   $171.55   $171.55   $171.60  
  Purchase #4 $157.54   6.232%   $167.3579   $167.36   $167.35   $167.40  
  Purchase #5 $66.34   6.545%   $70.682   $70.68   $70.70   $70.70  
  Purchase #6 $191.76   6.640%   $204.4929   $204.49   $204.50   $204.50  
  Purchase #7 $209.75   3.585%   $217.2695   $217.27   $217.25   $217.30  
  7 purchase totals = $1,110.43       $1,184.5431   $1,184.54   $1,184.55   $1,184.70