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	$89.40	3.240%	$92.2966	$92.30	$92.30	$92.30
Purchase #2	$149.31	10.230%	$164.5844	$164.58	$164.60	$164.60
Purchase #3	$123.42	10.571%	$136.4667	$136.47	$136.45	$136.50
Purchase #4	$45.69	12.804%	$51.5401	$51.54	$51.55	$51.50
Purchase #5	$195.57	10.451%	$216.009	$216.01	$216.00	$216.00
Purchase #6	$96.53	13.605%	$109.6629	$109.66	$109.65	$109.70
Purchase #7	$121.45	7.500%	$130.5588	$130.56	$130.55	$130.60
7 purchase totals =	$821.37		$901.1185	$901.12	$901.10	$901.20