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	$143.79	10.864%	$159.4113	$159.41	$159.40	$159.40
Purchase #2	$91.50	3.234%	$94.4591	$94.46	$94.45	$94.50
Purchase #3	$213.33	5.495%	$225.0525	$225.05	$225.05	$225.10
Purchase #4	$36.61	10.721%	$40.535	$40.54	$40.55	$40.50
Purchase #5	$201.31	6.565%	$214.526	$214.53	$214.55	$214.50
Purchase #6	$70.93	10.400%	$78.3067	$78.31	$78.30	$78.30
Purchase #7	$128.73	12.749%	$145.1418	$145.14	$145.15	$145.10
7 purchase totals =	$886.20		$957.4324	$957.44	$957.45	$957.40