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	$181.86	3.269%	$187.805	$187.81	$187.80	$187.80
Purchase #2	$111.72	4.325%	$116.5519	$116.55	$116.55	$116.60
Purchase #3	$126.26	13.209%	$142.9377	$142.94	$142.95	$142.90
Purchase #4	$90.54	9.471%	$99.115	$99.12	$99.10	$99.10
Purchase #5	$50.89	9.761%	$55.8574	$55.86	$55.85	$55.90
Purchase #6	$32.39	4.751%	$33.9288	$33.93	$33.95	$33.90
Purchase #7	$175.73	6.374%	$186.931	$186.93	$186.95	$186.90
7 purchase totals =	$769.39		$823.1268	$823.14	$823.15	$823.10