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	$143.57	3.281%	$148.2805	$148.28	$148.30	$148.30
Purchase #2	$223.94	11.841%	$250.4567	$250.46	$250.45	$250.50
Purchase #3	$206.40	4.848%	$216.4063	$216.41	$216.40	$216.40
Purchase #4	$11.94	3.398%	$12.3457	$12.35	$12.35	$12.30
Purchase #5	$37.35	11.831%	$41.7689	$41.77	$41.75	$41.80
Purchase #6	$158.42	11.500%	$176.6383	$176.64	$176.65	$176.60
Purchase #7	$80.80	7.563%	$86.9109	$86.91	$86.90	$86.90
7 purchase totals =	$862.42		$932.8073	$932.82	$932.80	$932.80