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 $84.95   13.874%   $96.736   $96.74   $96.75   $96.70  
  Purchase #2 $139.61   9.746%   $153.2164   $153.22   $153.20   $153.20  
  Purchase #3 $119.42   4.431%   $124.7115   $124.71   $124.70   $124.70  
  Purchase #4 $105.60   8.508%   $114.5844   $114.58   $114.60   $114.60  
  Purchase #5 $148.72   4.471%   $155.3693   $155.37   $155.35   $155.40  
  Purchase #6 $138.53   3.177%   $142.9311   $142.93   $142.95   $142.90  
  Purchase #7 $110.29   3.647%   $114.3123   $114.31   $114.30   $114.30  
  7 purchase totals = $847.12       $901.8610   $901.86   $901.85   $901.80