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	$181.87	3.846%	$188.8647	$188.86	$188.85	$188.90
Purchase #2	$55.39	4.588%	$57.9313	$57.93	$57.95	$57.90
Purchase #3	$136.40	10.273%	$150.4124	$150.41	$150.40	$150.40
Purchase #4	$45.60	12.582%	$51.3374	$51.34	$51.35	$51.30
Purchase #5	$223.77	11.412%	$249.3066	$249.31	$249.30	$249.30
Purchase #6	$197.58	9.531%	$216.4113	$216.41	$216.40	$216.40
Purchase #7	$217.39	12.357%	$244.2529	$244.25	$244.25	$244.30
7 purchase totals =	$1,058.00		$1,158.5166	$1,158.51	$1,158.50	$1,158.50