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	$156.33	12.262%	$175.4992	$175.50	$175.50	$175.50
Purchase #2	$134.64	4.518%	$140.723	$140.72	$140.70	$140.70
Purchase #3	$109.43	3.167%	$112.8956	$112.90	$112.90	$112.90
Purchase #4	$142.26	9.562%	$155.8629	$155.86	$155.85	$155.90
Purchase #5	$105.88	5.399%	$111.5965	$111.60	$111.60	$111.60
Purchase #6	$250.51	9.598%	$274.5539	$274.55	$274.55	$274.60
Purchase #7	$56.82	10.738%	$62.9213	$62.92	$62.90	$62.90
7 purchase totals =	$955.87		$1,034.0524	$1,034.05	$1,034.00	$1,034.10