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 $182.69   12.644%   $205.7893   $205.79   $205.80   $205.80  
  Purchase #2 $48.28   11.485%   $53.825   $53.83   $53.85   $53.80  
  Purchase #3 $221.61   10.792%   $245.5262   $245.53   $245.55   $245.50  
  Purchase #4 $174.96   8.561%   $189.9383   $189.94   $189.95   $189.90  
  Purchase #5 $39.79   13.715%   $45.2472   $45.25   $45.25   $45.20  
  Purchase #6 $213.25   9.425%   $233.3488   $233.35   $233.35   $233.30  
  Purchase #7 $249.37   11.670%   $278.4715   $278.47   $278.45   $278.50  
  7 purchase totals = $1,129.95       $1,252.1463   $1,252.16   $1,252.20   $1,252.00