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 $87.67   9.674%   $96.1512   $96.15   $96.15   $96.20  
  Purchase #2 $204.94   10.796%   $227.0653   $227.07   $227.05   $227.10  
  Purchase #3 $188.26   6.741%   $200.9506   $200.95   $200.95   $201.00  
  Purchase #4 $84.38   7.327%   $90.5625   $90.56   $90.55   $90.60  
  Purchase #5 $121.33   8.223%   $131.307   $131.31   $131.30   $131.30  
  Purchase #6 $201.75   8.757%   $219.4172   $219.42   $219.40   $219.40  
  Purchase #7 $183.90   7.206%   $197.1518   $197.15   $197.15   $197.20  
  7 purchase totals = $1,072.23       $1,162.6056   $1,162.61   $1,162.55   $1,162.80