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 $61.27   4.750%   $64.1803   $64.18   $64.20   $64.20  
  Purchase #2 $193.49   10.173%   $213.1737   $213.17   $213.15   $213.20  
  Purchase #3 $49.44   12.482%   $55.6111   $55.61   $55.60   $55.60  
  Purchase #4 $231.30   5.441%   $243.885   $243.89   $243.90   $243.90  
  Purchase #5 $11.95   8.636%   $12.982   $12.98   $13.00   $13.00  
  Purchase #6 $245.60   5.472%   $259.0392   $259.04   $259.05   $259.00  
  Purchase #7 $127.67   4.421%   $133.3143   $133.31   $133.30   $133.30  
  7 purchase totals = $920.72       $982.1856   $982.18   $982.20   $982.20