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 $236.33   13.739%   $268.7994   $268.80   $268.80   $268.80  
  Purchase #2 $186.35   11.848%   $208.4287   $208.43   $208.45   $208.40  
  Purchase #3 $46.40   9.871%   $50.9801   $50.98   $51.00   $51.00  
  Purchase #4 $32.98   6.874%   $35.247   $35.25   $35.25   $35.20  
  Purchase #5 $49.80   10.192%   $54.8756   $54.88   $54.90   $54.90  
  Purchase #6 $181.85   9.552%   $199.2203   $199.22   $199.20   $199.20  
  Purchase #7 $186.87   11.829%   $208.9749   $208.97   $208.95   $209.00  
  7 purchase totals = $920.58       $1,026.5260   $1,026.53   $1,026.55   $1,026.50