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 $32.57   6.377%   $34.647   $34.65   $34.65   $34.60  
  Purchase #2 $27.36   3.359%   $28.279   $28.28   $28.30   $28.30  
  Purchase #3 $244.67   9.384%   $267.6298   $267.63   $267.65   $267.60  
  Purchase #4 $58.71   7.665%   $63.2101   $63.21   $63.20   $63.20  
  Purchase #5 $160.77   13.636%   $182.6926   $182.69   $182.70   $182.70  
  Purchase #6 $50.47   5.759%   $53.3766   $53.38   $53.40   $53.40  
  Purchase #7 $119.51   3.799%   $124.0502   $124.05   $124.05   $124.10  
  7 purchase totals = $694.06       $753.8853   $753.89   $753.95   $753.90