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 $82.47   13.720%   $93.7849   $93.78   $93.80   $93.80  
  Purchase #2 $246.70   10.804%   $273.3535   $273.35   $273.35   $273.40  
  Purchase #3 $13.48   9.813%   $14.8028   $14.80   $14.80   $14.80  
  Purchase #4 $158.92   11.164%   $176.6618   $176.66   $176.65   $176.70  
  Purchase #5 $107.40   13.194%   $121.5704   $121.57   $121.55   $121.60  
  Purchase #6 $32.83   6.165%   $34.854   $34.85   $34.85   $34.90  
  Purchase #7 $128.64   11.367%   $143.2625   $143.26   $143.25   $143.30  
  7 purchase totals = $770.44       $858.2899   $858.27   $858.25   $858.50