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	$160.49	4.134%	$167.1247	$167.12	$167.10	$167.10
Purchase #2	$191.76	12.186%	$215.1279	$215.13	$215.15	$215.10
Purchase #3	$52.35	12.832%	$59.0676	$59.07	$59.05	$59.10
Purchase #4	$148.50	11.700%	$165.8745	$165.87	$165.85	$165.90
Purchase #5	$68.27	7.637%	$73.4838	$73.48	$73.50	$73.50
Purchase #6	$64.48	6.288%	$68.5345	$68.53	$68.55	$68.50
Purchase #7	$214.41	3.316%	$221.5198	$221.52	$221.50	$221.50
7 purchase totals =	$900.26		$970.7328	$970.72	$970.70	$970.70