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 $230.32   5.393%   $242.7412   $242.74   $242.75   $242.70  
  Purchase #2 $249.87   3.561%   $258.7679   $258.77   $258.75   $258.80  
  Purchase #3 $163.86   6.453%   $174.4339   $174.43   $174.45   $174.40  
  Purchase #4 $139.59   6.244%   $148.306   $148.31   $148.30   $148.30  
  Purchase #5 $86.46   11.313%   $96.2412   $96.24   $96.25   $96.20  
  Purchase #6 $165.27   5.241%   $173.9318   $173.93   $173.95   $173.90  
  Purchase #7 $158.26   11.210%   $176.0009   $176.00   $176.00   $176.00  
  7 purchase totals = $1,193.63       $1,270.4229   $1,270.42   $1,270.45   $1,270.30