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	$39.94	6.681%	$42.6084	$42.61	$42.60	$42.60
Purchase #2	$182.91	4.598%	$191.3202	$191.32	$191.30	$191.30
Purchase #3	$226.95	10.265%	$250.2464	$250.25	$250.25	$250.20
Purchase #4	$92.37	11.583%	$103.0692	$103.07	$103.05	$103.10
Purchase #5	$16.69	12.643%	$18.8001	$18.80	$18.80	$18.80
Purchase #6	$146.56	9.605%	$160.6371	$160.64	$160.65	$160.60
Purchase #7	$178.36	13.759%	$202.9006	$202.90	$202.90	$202.90
7 purchase totals =	$883.78		$969.5820	$969.59	$969.55	$969.50