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	$65.73	12.789%	$74.1362	$74.14	$74.15	$74.10
Purchase #2	$53.67	10.817%	$59.4755	$59.48	$59.50	$59.50
Purchase #3	$120.42	11.841%	$134.6789	$134.68	$134.70	$134.70
Purchase #4	$7.59	4.333%	$7.9189	$7.92	$7.90	$7.90
Purchase #5	$161.28	11.369%	$179.6159	$179.62	$179.60	$179.60
Purchase #6	$6.98	11.753%	$7.8004	$7.80	$7.80	$7.80
Purchase #7	$118.96	7.857%	$128.3067	$128.31	$128.30	$128.30
7 purchase totals =	$534.63		$591.9325	$591.95	$591.95	$591.90