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 $131.25   3.818%   $136.2611   $136.26   $136.25   $136.30  
  Purchase #2 $103.99   10.116%   $114.5096   $114.51   $114.50   $114.50  
  Purchase #3 $202.29   5.285%   $212.981   $212.98   $213.00   $213.00  
  Purchase #4 $24.65   8.511%   $26.748   $26.75   $26.75   $26.70  
  Purchase #5 $191.99   12.477%   $215.9446   $215.94   $215.95   $215.90  
  Purchase #6 $131.85   8.820%   $143.4792   $143.48   $143.50   $143.50  
  Purchase #7 $170.55   8.412%   $184.8967   $184.90   $184.90   $184.90  
  7 purchase totals = $956.57       $1,034.8202   $1,034.82   $1,034.85   $1,034.80