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 $232.47   13.124%   $262.9794   $262.98   $263.00   $263.00  
  Purchase #2 $12.48   3.111%   $12.8683   $12.87   $12.85   $12.90  
  Purchase #3 $156.92   6.664%   $167.3771   $167.38   $167.40   $167.40  
  Purchase #4 $138.65   5.714%   $146.5725   $146.57   $146.55   $146.60  
  Purchase #5 $109.60   13.519%   $124.4168   $124.42   $124.40   $124.40  
  Purchase #6 $196.96   10.759%   $218.1509   $218.15   $218.15   $218.20  
  Purchase #7 $237.87   11.787%   $265.9077   $265.91   $265.90   $265.90  
  7 purchase totals = $1,084.95       $1,198.2727   $1,198.28   $1,198.25   $1,198.40