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	$250.61	5.325%	$263.955	$263.96	$263.95	$264.00
Purchase #2	$134.45	5.117%	$141.3298	$141.33	$141.35	$141.30
Purchase #3	$18.87	13.458%	$21.4095	$21.41	$21.40	$21.40
Purchase #4	$29.29	8.152%	$31.6777	$31.68	$31.70	$31.70
Purchase #5	$6.72	10.844%	$7.4487	$7.45	$7.45	$7.40
Purchase #6	$247.73	6.272%	$263.2676	$263.27	$263.25	$263.30
Purchase #7	$64.43	13.228%	$72.9528	$72.95	$72.95	$73.00
7 purchase totals =	$752.10		$802.0411	$802.05	$802.05	$802.10