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 $91.67   5.462%   $96.677   $96.68   $96.70   $96.70  
  Purchase #2 $14.75   6.700%   $15.7383   $15.74   $15.75   $15.70  
  Purchase #3 $86.45   8.721%   $93.9893   $93.99   $94.00   $94.00  
  Purchase #4 $77.78   4.664%   $81.4077   $81.41   $81.40   $81.40  
  Purchase #5 $56.39   5.709%   $59.6093   $59.61   $59.60   $59.60  
  Purchase #6 $147.59   7.474%   $158.6209   $158.62   $158.60   $158.60  
  Purchase #7 $243.89   12.465%   $274.2909   $274.29   $274.30   $274.30  
  7 purchase totals = $718.52       $780.3334   $780.34   $780.35   $780.30