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 $61.86   6.303%   $65.759   $65.76   $65.75   $65.80  
  Purchase #2 $194.56   9.449%   $212.944   $212.94   $212.95   $212.90  
  Purchase #3 $30.39   5.318%   $32.0061   $32.01   $32.00   $32.00  
  Purchase #4 $130.28   8.564%   $141.4372   $141.44   $141.45   $141.40  
  Purchase #5 $86.71   9.486%   $94.9353   $94.94   $94.95   $94.90  
  Purchase #6 $8.33   8.516%   $9.0394   $9.04   $9.05   $9.00  
  Purchase #7 $218.55   7.691%   $235.3587   $235.36   $235.35   $235.40  
  7 purchase totals = $730.68       $791.4797   $791.49   $791.50   $791.40