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 $228.90   6.144%   $242.9636   $242.96   $242.95   $243.00  
  Purchase #2 $24.69   9.717%   $27.0891   $27.09   $27.10   $27.10  
  Purchase #3 $109.34   7.274%   $117.2934   $117.29   $117.30   $117.30  
  Purchase #4 $60.69   9.626%   $66.532   $66.53   $66.55   $66.50  
  Purchase #5 $129.73   4.723%   $135.8571   $135.86   $135.85   $135.90  
  Purchase #6 $101.75   13.745%   $115.7355   $115.74   $115.75   $115.70  
  Purchase #7 $232.60   3.670%   $241.1364   $241.14   $241.15   $241.10  
  7 purchase totals = $887.70       $946.6071   $946.61   $946.65   $946.60