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 $104.75   13.201%   $118.578   $118.58   $118.60   $118.60  
  Purchase #2 $64.49   9.205%   $70.4263   $70.43   $70.45   $70.40  
  Purchase #3 $99.79   13.571%   $113.3325   $113.33   $113.35   $113.30  
  Purchase #4 $45.87   3.547%   $47.497   $47.50   $47.50   $47.50  
  Purchase #5 $87.99   6.667%   $93.8563   $93.86   $93.85   $93.90  
  Purchase #6 $236.99   10.599%   $262.1086   $262.11   $262.10   $262.10  
  Purchase #7 $151.80   6.823%   $162.1573   $162.16   $162.15   $162.20  
  7 purchase totals = $791.68       $867.9560   $867.97   $868.00   $868.00