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 $217.77   11.402%   $242.6001   $242.60   $242.60   $242.60  
  Purchase #2 $40.85   4.492%   $42.685   $42.69   $42.70   $42.70  
  Purchase #3 $211.29   7.514%   $227.1663   $227.17   $227.15   $227.20  
  Purchase #4 $65.76   5.249%   $69.2117   $69.21   $69.20   $69.20  
  Purchase #5 $199.50   9.426%   $218.3049   $218.30   $218.30   $218.30  
  Purchase #6 $159.46   9.639%   $174.8303   $174.83   $174.85   $174.80  
  Purchase #7 $111.96   6.213%   $118.9161   $118.92   $118.90   $118.90  
  7 purchase totals = $1,006.59       $1,093.7144   $1,093.72   $1,093.70   $1,093.70