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 $55.99   8.448%   $60.72   $60.72   $60.70   $60.70  
  Purchase #2 $29.62   4.860%   $31.0595   $31.06   $31.05   $31.10  
  Purchase #3 $30.44   8.228%   $32.9446   $32.94   $32.95   $32.90  
  Purchase #4 $66.93   5.668%   $70.7236   $70.72   $70.70   $70.70  
  Purchase #5 $52.48   8.152%   $56.7582   $56.76   $56.75   $56.80  
  Purchase #6 $185.25   9.591%   $203.0173   $203.02   $203.00   $203.00  
  Purchase #7 $12.66   5.734%   $13.3859   $13.39   $13.40   $13.40  
  7 purchase totals = $433.37       $468.6091   $468.61   $468.55   $468.60