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 $99.71   11.467%   $111.1437   $111.14   $111.15   $111.10  
  Purchase #2 $88.42   5.589%   $93.3618   $93.36   $93.35   $93.40  
  Purchase #3 $35.38   3.525%   $36.6271   $36.63   $36.65   $36.60  
  Purchase #4 $121.81   3.492%   $126.0636   $126.06   $126.05   $126.10  
  Purchase #5 $244.62   5.744%   $258.671   $258.67   $258.65   $258.70  
  Purchase #6 $237.33   6.552%   $252.8799   $252.88   $252.90   $252.90  
  Purchase #7 $81.28   10.591%   $89.8884   $89.89   $89.90   $89.90  
  7 purchase totals = $908.55       $968.6355   $968.63   $968.65   $968.70