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 $197.36   8.564%   $214.2619   $214.26   $214.25   $214.30  
  Purchase #2 $204.77   10.311%   $225.8838   $225.88   $225.90   $225.90  
  Purchase #3 $204.50   12.662%   $230.3938   $230.39   $230.40   $230.40  
  Purchase #4 $62.64   12.153%   $70.2526   $70.25   $70.25   $70.30  
  Purchase #5 $62.54   11.798%   $69.9185   $69.92   $69.90   $69.90  
  Purchase #6 $102.98   11.644%   $114.971   $114.97   $114.95   $115.00  
  Purchase #7 $68.35   6.733%   $72.952   $72.95   $72.95   $73.00  
  7 purchase totals = $903.14       $998.6336   $998.62   $998.60   $998.80