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 $43.98   11.510%   $49.0421   $49.04   $49.05   $49.00  
  Purchase #2 $104.85   8.424%   $113.6826   $113.68   $113.70   $113.70  
  Purchase #3 $155.77   4.854%   $163.3311   $163.33   $163.35   $163.30  
  Purchase #4 $207.63   4.806%   $217.6087   $217.61   $217.60   $217.60  
  Purchase #5 $187.93   12.542%   $211.5002   $211.50   $211.50   $211.50  
  Purchase #6 $162.55   12.492%   $182.8557   $182.86   $182.85   $182.90  
  Purchase #7 $85.70   7.872%   $92.4463   $92.45   $92.45   $92.40  
  7 purchase totals = $948.41       $1,030.4667   $1,030.47   $1,030.50   $1,030.40