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 $68.91   11.847%   $77.0738   $77.07   $77.05   $77.10  
  Purchase #2 $188.25   3.467%   $194.7766   $194.78   $194.80   $194.80  
  Purchase #3 $243.71   5.551%   $257.2383   $257.24   $257.25   $257.20  
  Purchase #4 $237.49   9.840%   $260.859   $260.86   $260.85   $260.90  
  Purchase #5 $125.32   12.679%   $141.2093   $141.21   $141.20   $141.20  
  Purchase #6 $32.84   6.298%   $34.9083   $34.91   $34.90   $34.90  
  Purchase #7 $33.95   11.817%   $37.9619   $37.96   $37.95   $38.00  
  7 purchase totals = $930.47       $1,004.0272   $1,004.03   $1,004.00   $1,004.10