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	$218.41	4.717%	$228.7124	$228.71	$228.70	$228.70
Purchase #2	$104.53	4.468%	$109.2004	$109.20	$109.20	$109.20
Purchase #3	$117.82	5.584%	$124.3991	$124.40	$124.40	$124.40
Purchase #4	$181.58	8.179%	$196.4314	$196.43	$196.45	$196.40
Purchase #5	$74.74	6.149%	$79.3358	$79.34	$79.35	$79.30
Purchase #6	$72.77	13.519%	$82.6078	$82.61	$82.60	$82.60
Purchase #7	$153.72	4.234%	$160.2285	$160.23	$160.25	$160.20
7 purchase totals =	$923.57		$980.9154	$980.92	$980.95	$980.80