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 $223.49   13.539%   $253.7483   $253.75   $253.75   $253.70  
  Purchase #2 $87.71   12.163%   $98.3782   $98.38   $98.40   $98.40  
  Purchase #3 $63.45   8.561%   $68.882   $68.88   $68.90   $68.90  
  Purchase #4 $245.54   12.721%   $276.7751   $276.78   $276.80   $276.80  
  Purchase #5 $92.25   13.535%   $104.736   $104.74   $104.75   $104.70  
  Purchase #6 $207.45   7.333%   $222.6623   $222.66   $222.65   $222.70  
  Purchase #7 $181.64   4.148%   $189.1744   $189.17   $189.15   $189.20  
  7 purchase totals = $1,101.53       $1,214.3563   $1,214.36   $1,214.40   $1,214.40