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	$234.81	6.863%	$250.925	$250.93	$250.95	$250.90
Purchase #2	$146.71	8.614%	$159.3476	$159.35	$159.35	$159.30
Purchase #3	$181.94	5.377%	$191.7229	$191.72	$191.70	$191.70
Purchase #4	$96.63	13.250%	$109.4335	$109.43	$109.45	$109.40
Purchase #5	$202.48	5.309%	$213.2297	$213.23	$213.25	$213.20
Purchase #6	$202.30	10.673%	$223.8915	$223.89	$223.90	$223.90
Purchase #7	$9.76	6.787%	$10.4224	$10.42	$10.40	$10.40
7 purchase totals =	$1,074.63		$1,158.9726	$1,158.97	$1,159.00	$1,158.80