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 $143.96   5.356%   $151.6705   $151.67   $151.65   $151.70  
  Purchase #2 $186.76   4.179%   $194.5647   $194.56   $194.55   $194.60  
  Purchase #3 $93.41   6.575%   $99.5517   $99.55   $99.55   $99.60  
  Purchase #4 $52.49   6.191%   $55.7397   $55.74   $55.75   $55.70  
  Purchase #5 $217.44   11.307%   $242.0259   $242.03   $242.05   $242.00  
  Purchase #6 $22.53   8.198%   $24.377   $24.38   $24.40   $24.40  
  Purchase #7 $232.33   11.577%   $259.2268   $259.23   $259.25   $259.20  
  7 purchase totals = $948.92       $1,027.1563   $1,027.16   $1,027.20   $1,027.20