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	$117.52	10.825%	$130.2415	$130.24	$130.25	$130.20
Purchase #2	$208.74	8.242%	$225.9444	$225.94	$225.95	$225.90
Purchase #3	$192.59	11.133%	$214.031	$214.03	$214.05	$214.00
Purchase #4	$101.35	4.230%	$105.6371	$105.64	$105.65	$105.60
Purchase #5	$182.71	9.313%	$199.7258	$199.73	$199.75	$199.70
Purchase #6	$161.89	11.510%	$180.5235	$180.52	$180.50	$180.50
Purchase #7	$31.38	12.384%	$35.2661	$35.27	$35.25	$35.30
7 purchase totals =	$996.18		$1,091.3694	$1,091.37	$1,091.40	$1,091.20