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 $80.98   6.234%   $86.0283   $86.03   $86.05   $86.00  
  Purchase #2 $24.63   5.773%   $26.0519   $26.05   $26.05   $26.10  
  Purchase #3 $200.88   8.675%   $218.3063   $218.31   $218.30   $218.30  
  Purchase #4 $178.31   12.155%   $199.9836   $199.98   $200.00   $200.00  
  Purchase #5 $246.74   10.742%   $273.2448   $273.24   $273.25   $273.20  
  Purchase #6 $174.37   11.540%   $194.4923   $194.49   $194.50   $194.50  
  Purchase #7 $205.33   6.570%   $218.8202   $218.82   $218.80   $218.80  
  7 purchase totals = $1,111.24       $1,216.9274   $1,216.92   $1,216.95   $1,216.90