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	$87.59	13.573%	$99.4786	$99.48	$99.50	$99.50
Purchase #2	$179.43	8.515%	$194.7085	$194.71	$194.70	$194.70
Purchase #3	$152.74	10.124%	$168.2034	$168.20	$168.20	$168.20
Purchase #4	$40.77	6.677%	$43.4922	$43.49	$43.50	$43.50
Purchase #5	$245.97	13.345%	$278.7947	$278.79	$278.80	$278.80
Purchase #6	$92.97	8.822%	$101.1718	$101.17	$101.15	$101.20
Purchase #7	$117.41	11.137%	$130.486	$130.49	$130.50	$130.50
7 purchase totals =	$916.88		$1,016.3352	$1,016.33	$1,016.35	$1,016.40