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 $246.43   8.733%   $267.9507   $267.95   $267.95   $268.00  
  Purchase #2 $63.77   3.496%   $65.9994   $66.00   $66.00   $66.00  
  Purchase #3 $210.59   6.721%   $224.7438   $224.74   $224.75   $224.70  
  Purchase #4 $149.64   5.723%   $158.2039   $158.20   $158.20   $158.20  
  Purchase #5 $230.62   9.715%   $253.0247   $253.02   $253.00   $253.00  
  Purchase #6 $205.84   12.668%   $231.9158   $231.92   $231.90   $231.90  
  Purchase #7 $236.84   8.233%   $256.339   $256.34   $256.35   $256.30  
  7 purchase totals = $1,343.73       $1,458.1773   $1,458.17   $1,458.15   $1,458.10