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	$217.40	12.387%	$244.3293	$244.33	$244.35	$244.30
Purchase #2	$100.84	4.468%	$105.3455	$105.35	$105.35	$105.30
Purchase #3	$223.52	8.481%	$242.4767	$242.48	$242.50	$242.50
Purchase #4	$182.90	5.570%	$193.0875	$193.09	$193.10	$193.10
Purchase #5	$67.52	7.296%	$72.4463	$72.45	$72.45	$72.40
Purchase #6	$131.46	11.104%	$146.0573	$146.06	$146.05	$146.10
Purchase #7	$245.92	11.157%	$273.3573	$273.36	$273.35	$273.40
7 purchase totals =	$1,169.56		$1,277.0999	$1,277.12	$1,277.15	$1,277.10