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	$42.40	6.790%	$45.279	$45.28	$45.30	$45.30
Purchase #2	$97.87	5.415%	$103.1697	$103.17	$103.15	$103.20
Purchase #3	$240.66	4.506%	$251.5041	$251.50	$251.50	$251.50
Purchase #4	$12.51	5.830%	$13.2393	$13.24	$13.25	$13.20
Purchase #5	$90.27	4.843%	$94.6418	$94.64	$94.65	$94.60
Purchase #6	$54.26	4.406%	$56.6507	$56.65	$56.65	$56.70
Purchase #7	$200.61	7.380%	$215.415	$215.42	$215.40	$215.40
7 purchase totals =	$738.58		$779.8996	$779.90	$779.90	$779.90