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 $164.76   12.463%   $185.294   $185.29   $185.30   $185.30  
  Purchase #2 $33.51   3.539%   $34.6959   $34.70   $34.70   $34.70  
  Purchase #3 $161.26   7.498%   $173.3513   $173.35   $173.35   $173.40  
  Purchase #4 $147.72   5.870%   $156.3912   $156.39   $156.40   $156.40  
  Purchase #5 $62.81   5.227%   $66.0931   $66.09   $66.10   $66.10  
  Purchase #6 $139.66   4.450%   $145.8749   $145.87   $145.85   $145.90  
  Purchase #7 $213.87   7.298%   $229.4782   $229.48   $229.50   $229.50  
  7 purchase totals = $923.59       $991.1786   $991.17   $991.20   $991.30