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	$223.86	6.639%	$238.7221	$238.72	$238.70	$238.70
Purchase #2	$207.99	7.424%	$223.4312	$223.43	$223.45	$223.40
Purchase #3	$62.32	3.379%	$64.4258	$64.43	$64.45	$64.40
Purchase #4	$27.29	7.445%	$29.3217	$29.32	$29.30	$29.30
Purchase #5	$98.58	11.837%	$110.2489	$110.25	$110.25	$110.20
Purchase #6	$92.86	7.388%	$99.7205	$99.72	$99.70	$99.70
Purchase #7	$109.47	7.165%	$117.3135	$117.31	$117.30	$117.30
7 purchase totals =	$822.37		$883.1837	$883.18	$883.15	$883.00