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 $62.87   10.611%   $69.5411   $69.54   $69.55   $69.50  
  Purchase #2 $68.86   12.761%   $77.6472   $77.65   $77.65   $77.60  
  Purchase #3 $116.42   3.823%   $120.8707   $120.87   $120.85   $120.90  
  Purchase #4 $97.32   11.588%   $108.5974   $108.60   $108.60   $108.60  
  Purchase #5 $121.54   12.647%   $136.9112   $136.91   $136.90   $136.90  
  Purchase #6 $122.35   10.541%   $135.2469   $135.25   $135.25   $135.20  
  Purchase #7 $216.47   11.272%   $240.8705   $240.87   $240.85   $240.90  
  7 purchase totals = $805.83       $889.6850   $889.69   $889.65   $889.60