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 $126.95   11.485%   $141.5302   $141.53   $141.55   $141.50  
  Purchase #2 $142.48   8.556%   $154.6706   $154.67   $154.65   $154.70  
  Purchase #3 $231.58   6.871%   $247.4919   $247.49   $247.50   $247.50  
  Purchase #4 $43.50   8.826%   $47.3393   $47.34   $47.35   $47.30  
  Purchase #5 $141.37   9.179%   $154.3464   $154.35   $154.35   $154.30  
  Purchase #6 $43.59   11.573%   $48.6347   $48.63   $48.65   $48.60  
  Purchase #7 $73.95   10.829%   $81.958   $81.96   $81.95   $82.00  
  7 purchase totals = $803.42       $875.9711   $875.97   $876.00   $875.90