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 $187.45   10.872%   $207.8296   $207.83   $207.85   $207.80  
  Purchase #2 $135.64   11.564%   $151.3254   $151.33   $151.35   $151.30  
  Purchase #3 $140.33   13.862%   $159.7825   $159.78   $159.80   $159.80  
  Purchase #4 $236.59   12.752%   $266.76   $266.76   $266.75   $266.80  
  Purchase #5 $242.47   13.393%   $274.944   $274.94   $274.95   $274.90  
  Purchase #6 $101.28   5.545%   $106.896   $106.90   $106.90   $106.90  
  Purchase #7 $192.77   6.452%   $205.2075   $205.21   $205.20   $205.20  
  7 purchase totals = $1,236.53       $1,372.7450   $1,372.75   $1,372.80   $1,372.70