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	$123.68	4.539%	$129.2938	$129.29	$129.30	$129.30
Purchase #2	$78.70	9.655%	$86.2985	$86.30	$86.30	$86.30
Purchase #3	$148.60	7.687%	$160.0229	$160.02	$160.00	$160.00
Purchase #4	$238.77	5.423%	$251.7185	$251.72	$251.70	$251.70
Purchase #5	$29.74	12.521%	$33.4637	$33.46	$33.45	$33.50
Purchase #6	$109.59	8.504%	$118.9095	$118.91	$118.90	$118.90
Purchase #7	$67.48	7.442%	$72.5019	$72.50	$72.50	$72.50
7 purchase totals =	$796.56		$852.2088	$852.20	$852.15	$852.20