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	$110.70	11.273%	$123.1792	$123.18	$123.20	$123.20
Purchase #2	$57.61	13.114%	$65.165	$65.17	$65.15	$65.20
Purchase #3	$172.90	11.666%	$193.0705	$193.07	$193.05	$193.10
Purchase #4	$57.36	6.400%	$61.031	$61.03	$61.05	$61.00
Purchase #5	$34.44	9.385%	$37.6722	$37.67	$37.65	$37.70
Purchase #6	$187.40	11.230%	$208.445	$208.45	$208.45	$208.40
Purchase #7	$53.56	3.299%	$55.3269	$55.33	$55.35	$55.30
7 purchase totals =	$673.97		$743.8898	$743.90	$743.90	$743.90