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 $84.53   13.758%   $96.1596   $96.16   $96.15   $96.20  
  Purchase #2 $146.40   10.333%   $161.5275   $161.53   $161.55   $161.50  
  Purchase #3 $92.76   13.157%   $104.9644   $104.96   $104.95   $105.00  
  Purchase #4 $194.70   7.137%   $208.5957   $208.60   $208.60   $208.60  
  Purchase #5 $68.34   6.855%   $73.0247   $73.02   $73.00   $73.00  
  Purchase #6 $172.37   6.338%   $183.2948   $183.29   $183.30   $183.30  
  Purchase #7 $29.66   13.213%   $33.579   $33.58   $33.60   $33.60  
  7 purchase totals = $788.76       $861.1457   $861.14   $861.15   $861.20