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 $22.29   11.729%   $24.9044   $24.90   $24.90   $24.90  
  Purchase #2 $114.39   10.861%   $126.8139   $126.81   $126.80   $126.80  
  Purchase #3 $22.39   10.175%   $24.6682   $24.67   $24.65   $24.70  
  Purchase #4 $149.44   5.476%   $157.6233   $157.62   $157.60   $157.60  
  Purchase #5 $70.68   3.325%   $73.0301   $73.03   $73.05   $73.00  
  Purchase #6 $211.47   3.769%   $219.4403   $219.44   $219.45   $219.40  
  Purchase #7 $173.86   13.770%   $197.8005   $197.80   $197.80   $197.80  
  7 purchase totals = $764.52       $824.2807   $824.27   $824.25   $824.20