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 $100.87   7.870%   $108.8085   $108.81   $108.80   $108.80  
  Purchase #2 $19.49   8.245%   $21.097   $21.10   $21.10   $21.10  
  Purchase #3 $108.55   5.284%   $114.2858   $114.29   $114.30   $114.30  
  Purchase #4 $128.62   6.331%   $136.7629   $136.76   $136.75   $136.80  
  Purchase #5 $156.67   4.375%   $163.5243   $163.52   $163.50   $163.50  
  Purchase #6 $162.94   10.238%   $179.6218   $179.62   $179.60   $179.60  
  Purchase #7 $51.44   6.697%   $54.8849   $54.88   $54.90   $54.90  
  7 purchase totals = $728.58       $778.9852   $778.98   $778.95   $779.00