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 $66.39   13.635%   $75.4423   $75.44   $75.45   $75.40  
  Purchase #2 $39.95   6.636%   $42.6011   $42.60   $42.60   $42.60  
  Purchase #3 $27.41   4.689%   $28.6953   $28.70   $28.70   $28.70  
  Purchase #4 $204.78   5.484%   $216.0101   $216.01   $216.00   $216.00  
  Purchase #5 $240.60   10.844%   $266.6907   $266.69   $266.70   $266.70  
  Purchase #6 $168.64   3.333%   $174.2608   $174.26   $174.25   $174.30  
  Purchase #7 $195.94   11.463%   $218.4006   $218.40   $218.40   $218.40  
  7 purchase totals = $943.71       $1,022.1009   $1,022.10   $1,022.10   $1,022.10