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 $246.51   3.684%   $255.5914   $255.59   $255.60   $255.60  
  Purchase #2 $30.85   3.368%   $31.889   $31.89   $31.90   $31.90  
  Purchase #3 $33.73   9.421%   $36.9077   $36.91   $36.90   $36.90  
  Purchase #4 $186.73   7.573%   $200.8711   $200.87   $200.85   $200.90  
  Purchase #5 $130.80   10.819%   $144.9513   $144.95   $144.95   $145.00  
  Purchase #6 $169.82   13.646%   $192.9936   $192.99   $193.00   $193.00  
  Purchase #7 $152.80   13.227%   $173.0109   $173.01   $173.00   $173.00  
  7 purchase totals = $951.24       $1,036.2150   $1,036.21   $1,036.20   $1,036.30