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 $8.84   8.550%   $9.5958   $9.60   $9.60   $9.60  
  Purchase #2 $171.73   7.119%   $183.9555   $183.96   $183.95   $184.00  
  Purchase #3 $73.36   11.283%   $81.6372   $81.64   $81.65   $81.60  
  Purchase #4 $194.38   11.655%   $217.035   $217.04   $217.05   $217.00  
  Purchase #5 $90.94   13.111%   $102.8631   $102.86   $102.85   $102.90  
  Purchase #6 $131.63   6.183%   $139.7687   $139.77   $139.75   $139.80  
  Purchase #7 $193.42   8.782%   $210.4061   $210.41   $210.40   $210.40  
  7 purchase totals = $864.30       $945.2614   $945.28   $945.25   $945.30