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 $24.67   5.419%   $26.0069   $26.01   $26.00   $26.00  
  Purchase #2 $126.67   10.316%   $139.7373   $139.74   $139.75   $139.70  
  Purchase #3 $94.51   7.393%   $101.4971   $101.50   $101.50   $101.50  
  Purchase #4 $38.45   5.856%   $40.7016   $40.70   $40.70   $40.70  
  Purchase #5 $229.95   8.740%   $250.0476   $250.05   $250.05   $250.00  
  Purchase #6 $31.92   12.275%   $35.8382   $35.84   $35.85   $35.80  
  Purchase #7 $185.59   6.775%   $198.1637   $198.16   $198.15   $198.20  
  7 purchase totals = $731.76       $791.9924   $792.00   $792.00   $791.90