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	$53.38	4.164%	$55.6027	$55.60	$55.60	$55.60
Purchase #2	$131.76	7.819%	$142.0623	$142.06	$142.05	$142.10
Purchase #3	$192.59	7.241%	$206.5354	$206.54	$206.55	$206.50
Purchase #4	$18.90	11.126%	$21.0028	$21.00	$21.00	$21.00
Purchase #5	$86.79	8.260%	$93.9589	$93.96	$93.95	$94.00
Purchase #6	$15.89	13.742%	$18.0736	$18.07	$18.05	$18.10
Purchase #7	$40.75	11.677%	$45.5084	$45.51	$45.50	$45.50
7 purchase totals =	$540.06		$582.7441	$582.74	$582.70	$582.80