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 $248.55   10.373%   $274.3321   $274.33   $274.35   $274.30  
  Purchase #2 $115.37   8.606%   $125.2987   $125.30   $125.30   $125.30  
  Purchase #3 $86.42   5.816%   $91.4462   $91.45   $91.45   $91.40  
  Purchase #4 $195.25   5.560%   $206.1059   $206.11   $206.10   $206.10  
  Purchase #5 $111.87   5.503%   $118.0262   $118.03   $118.05   $118.00  
  Purchase #6 $189.50   8.812%   $206.1987   $206.20   $206.20   $206.20  
  Purchase #7 $39.95   5.318%   $42.0745   $42.07   $42.05   $42.10  
  7 purchase totals = $986.91       $1,063.4823   $1,063.49   $1,063.50   $1,063.40