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 $246.40   6.211%   $261.7039   $261.70   $261.70   $261.70  
  Purchase #2 $125.62   11.135%   $139.6078   $139.61   $139.60   $139.60  
  Purchase #3 $17.74   12.820%   $20.0143   $20.01   $20.00   $20.00  
  Purchase #4 $190.91   11.551%   $212.962   $212.96   $212.95   $213.00  
  Purchase #5 $29.58   5.817%   $31.3007   $31.30   $31.30   $31.30  
  Purchase #6 $147.66   6.490%   $157.2431   $157.24   $157.25   $157.20  
  Purchase #7 $159.91   8.177%   $172.9858   $172.99   $173.00   $173.00  
  7 purchase totals = $917.82       $995.8176   $995.81   $995.80   $995.80