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 $79.45   3.539%   $82.2617   $82.26   $82.25   $82.30  
  Purchase #2 $165.67   9.381%   $181.2115   $181.21   $181.20   $181.20  
  Purchase #3 $184.74   12.442%   $207.7254   $207.73   $207.75   $207.70  
  Purchase #4 $190.98   7.594%   $205.483   $205.48   $205.50   $205.50  
  Purchase #5 $96.29   8.633%   $104.6027   $104.60   $104.60   $104.60  
  Purchase #6 $63.84   4.443%   $66.6764   $66.68   $66.70   $66.70  
  Purchase #7 $101.92   12.214%   $114.3685   $114.37   $114.35   $114.40  
  7 purchase totals = $882.89       $962.3292   $962.33   $962.35   $962.40