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	$159.71	7.316%	$171.3944	$171.39	$171.40	$171.40
Purchase #2	$244.43	12.839%	$275.8124	$275.81	$275.80	$275.80
Purchase #3	$240.99	13.563%	$273.6755	$273.68	$273.70	$273.70
Purchase #4	$120.57	6.544%	$128.4601	$128.46	$128.45	$128.50
Purchase #5	$179.69	4.651%	$188.0474	$188.05	$188.05	$188.00
Purchase #6	$52.71	13.662%	$59.9112	$59.91	$59.90	$59.90
Purchase #7	$244.48	10.864%	$271.0403	$271.04	$271.05	$271.00
7 purchase totals =	$1,242.58		$1,368.3413	$1,368.34	$1,368.35	$1,368.30