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 $14.40   8.670%   $15.6485   $15.65   $15.65   $15.60  
  Purchase #2 $182.78   10.198%   $201.4199   $201.42   $201.40   $201.40  
  Purchase #3 $221.31   10.340%   $244.1935   $244.19   $244.20   $244.20  
  Purchase #4 $66.58   10.771%   $73.7513   $73.75   $73.75   $73.80  
  Purchase #5 $178.88   4.429%   $186.8026   $186.80   $186.80   $186.80  
  Purchase #6 $133.93   9.610%   $146.8007   $146.80   $146.80   $146.80  
  Purchase #7 $182.74   12.843%   $206.2093   $206.21   $206.20   $206.20  
  7 purchase totals = $980.62       $1,074.8258   $1,074.82   $1,074.80   $1,074.80