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	$37.37	12.258%	$41.9508	$41.95	$41.95	$42.00
Purchase #2	$147.33	4.272%	$153.6239	$153.62	$153.60	$153.60
Purchase #3	$52.38	3.842%	$54.3924	$54.39	$54.40	$54.40
Purchase #4	$85.86	13.341%	$97.3146	$97.31	$97.30	$97.30
Purchase #5	$68.73	4.305%	$71.6888	$71.69	$71.70	$71.70
Purchase #6	$211.80	8.327%	$229.4366	$229.44	$229.45	$229.40
Purchase #7	$156.50	10.280%	$172.5882	$172.59	$172.60	$172.60
7 purchase totals =	$759.97		$820.9953	$820.99	$821.00	$821.00