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 $113.43   5.382%   $119.5348   $119.53   $119.55   $119.50  
  Purchase #2 $148.61   3.565%   $153.9079   $153.91   $153.90   $153.90  
  Purchase #3 $242.74   8.733%   $263.9385   $263.94   $263.95   $263.90  
  Purchase #4 $138.98   9.297%   $151.901   $151.90   $151.90   $151.90  
  Purchase #5 $86.77   9.816%   $95.2873   $95.29   $95.30   $95.30  
  Purchase #6 $191.33   6.693%   $204.1357   $204.14   $204.15   $204.10  
  Purchase #7 $26.70   7.396%   $28.6747   $28.67   $28.65   $28.70  
  7 purchase totals = $948.56       $1,017.3799   $1,017.38   $1,017.40   $1,017.30