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 $93.62   5.646%   $98.9058   $98.91   $98.90   $98.90  
  Purchase #2 $241.55   10.345%   $266.5383   $266.54   $266.55   $266.50  
  Purchase #3 $235.72   13.207%   $266.8515   $266.85   $266.85   $266.90  
  Purchase #4 $68.95   3.806%   $71.5742   $71.57   $71.55   $71.60  
  Purchase #5 $154.97   13.464%   $175.8352   $175.84   $175.85   $175.80  
  Purchase #6 $246.45   5.627%   $260.3177   $260.32   $260.30   $260.30  
  Purchase #7 $63.38   5.103%   $66.6143   $66.61   $66.60   $66.60  
  7 purchase totals = $1,104.64       $1,206.6370   $1,206.64   $1,206.60   $1,206.60