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 $195.93   4.257%   $204.2707   $204.27   $204.25   $204.30  
  Purchase #2 $144.55   11.858%   $161.6907   $161.69   $161.70   $161.70  
  Purchase #3 $241.32   12.771%   $272.139   $272.14   $272.15   $272.10  
  Purchase #4 $69.29   4.345%   $72.3007   $72.30   $72.30   $72.30  
  Purchase #5 $27.61   6.432%   $29.3859   $29.39   $29.40   $29.40  
  Purchase #6 $196.96   13.583%   $223.7131   $223.71   $223.70   $223.70  
  Purchase #7 $239.53   10.367%   $264.3621   $264.36   $264.35   $264.40  
  7 purchase totals = $1,115.19       $1,227.8622   $1,227.86   $1,227.85   $1,227.90