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 $63.53   3.863%   $65.9842   $65.98   $66.00   $66.00  
  Purchase #2 $200.98   9.340%   $219.7515   $219.75   $219.75   $219.80  
  Purchase #3 $90.88   4.764%   $95.2095   $95.21   $95.20   $95.20  
  Purchase #4 $39.29   8.675%   $42.6984   $42.70   $42.70   $42.70  
  Purchase #5 $37.60   5.382%   $39.6236   $39.62   $39.60   $39.60  
  Purchase #6 $245.27   6.668%   $261.6246   $261.62   $261.60   $261.60  
  Purchase #7 $14.69   3.656%   $15.2271   $15.23   $15.25   $15.20  
  7 purchase totals = $692.24       $740.1189   $740.11   $740.10   $740.10