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	$197.49	13.340%	$223.8352	$223.84	$223.85	$223.80
Purchase #2	$237.59	11.504%	$264.9224	$264.92	$264.90	$264.90
Purchase #3	$218.89	12.730%	$246.7547	$246.75	$246.75	$246.80
Purchase #4	$114.88	7.422%	$123.4064	$123.41	$123.40	$123.40
Purchase #5	$228.78	13.167%	$258.9035	$258.90	$258.90	$258.90
Purchase #6	$185.42	3.384%	$191.6946	$191.69	$191.70	$191.70
Purchase #7	$79.67	8.785%	$86.669	$86.67	$86.65	$86.70
7 purchase totals =	$1,262.72		$1,396.1858	$1,396.18	$1,396.15	$1,396.20