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 $62.28   9.606%   $68.2626   $68.26   $68.25   $68.30  
  Purchase #2 $109.39   13.755%   $124.4366   $124.44   $124.45   $124.40  
  Purchase #3 $146.77   11.468%   $163.6016   $163.60   $163.60   $163.60  
  Purchase #4 $63.82   8.223%   $69.0679   $69.07   $69.05   $69.10  
  Purchase #5 $209.40   8.170%   $226.508   $226.51   $226.50   $226.50  
  Purchase #6 $203.55   5.820%   $215.3966   $215.40   $215.40   $215.40  
  Purchase #7 $7.48   7.637%   $8.0512   $8.05   $8.05   $8.10  
  7 purchase totals = $802.69       $875.3245   $875.33   $875.30   $875.40