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	$9.94	3.171%	$10.2552	$10.26	$10.25	$10.30
Purchase #2	$233.81	7.243%	$250.7449	$250.74	$250.75	$250.70
Purchase #3	$53.78	10.233%	$59.2833	$59.28	$59.30	$59.30
Purchase #4	$193.64	13.384%	$219.5568	$219.56	$219.55	$219.60
Purchase #5	$84.77	7.341%	$90.993	$90.99	$91.00	$91.00
Purchase #6	$110.44	12.701%	$124.467	$124.47	$124.45	$124.50
Purchase #7	$80.87	11.585%	$90.2388	$90.24	$90.25	$90.20
7 purchase totals =	$767.25		$845.5390	$845.54	$845.55	$845.60