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	$37.74	3.479%	$39.053	$39.05	$39.05	$39.10
Purchase #2	$248.42	3.247%	$256.4862	$256.49	$256.50	$256.50
Purchase #3	$238.90	12.591%	$268.9799	$268.98	$269.00	$269.00
Purchase #4	$196.61	13.694%	$223.5338	$223.53	$223.55	$223.50
Purchase #5	$131.77	5.734%	$139.3257	$139.33	$139.35	$139.30
Purchase #6	$149.76	11.315%	$166.7053	$166.71	$166.70	$166.70
Purchase #7	$123.49	13.679%	$140.3822	$140.38	$140.40	$140.40
7 purchase totals =	$1,126.69		$1,234.4661	$1,234.47	$1,234.55	$1,234.50