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	$240.95	9.817%	$264.6041	$264.60	$264.60	$264.60
Purchase #2	$219.92	11.781%	$245.8288	$245.83	$245.85	$245.80
Purchase #3	$183.89	3.591%	$190.4935	$190.49	$190.50	$190.50
Purchase #4	$88.83	12.367%	$99.8156	$99.82	$99.80	$99.80
Purchase #5	$230.90	12.173%	$259.0075	$259.01	$259.00	$259.00
Purchase #6	$124.80	10.192%	$137.5196	$137.52	$137.50	$137.50
Purchase #7	$109.30	8.640%	$118.7435	$118.74	$118.75	$118.70
7 purchase totals =	$1,198.59		$1,316.0126	$1,316.01	$1,316.00	$1,315.90