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	$156.97	12.783%	$177.0355	$177.04	$177.05	$177.00
Purchase #2	$71.61	12.554%	$80.5999	$80.60	$80.60	$80.60
Purchase #3	$145.84	6.485%	$155.2977	$155.30	$155.30	$155.30
Purchase #4	$167.46	10.810%	$185.5624	$185.56	$185.55	$185.60
Purchase #5	$159.43	7.129%	$170.7958	$170.80	$170.80	$170.80
Purchase #6	$136.39	8.843%	$148.451	$148.45	$148.45	$148.50
Purchase #7	$200.57	11.253%	$223.1401	$223.14	$223.15	$223.10
7 purchase totals =	$1,038.27		$1,140.8824	$1,140.89	$1,140.90	$1,140.90