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 $68.29   12.658%   $76.9341   $76.93   $76.95   $76.90  
  Purchase #2 $149.90   8.412%   $162.5096   $162.51   $162.50   $162.50  
  Purchase #3 $229.85   10.741%   $254.5382   $254.54   $254.55   $254.50  
  Purchase #4 $83.59   9.858%   $91.8303   $91.83   $91.85   $91.80  
  Purchase #5 $126.79   5.458%   $133.7102   $133.71   $133.70   $133.70  
  Purchase #6 $221.52   8.671%   $240.728   $240.73   $240.75   $240.70  
  Purchase #7 $182.62   3.250%   $188.5552   $188.56   $188.55   $188.60  
  7 purchase totals = $1,062.56       $1,148.8056   $1,148.81   $1,148.85   $1,148.70