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	$128.64	6.157%	$136.5604	$136.56	$136.55	$136.60
Purchase #2	$66.97	7.131%	$71.7456	$71.75	$71.75	$71.70
Purchase #3	$200.54	12.378%	$225.3628	$225.36	$225.35	$225.40
Purchase #4	$121.52	13.487%	$137.9094	$137.91	$137.90	$137.90
Purchase #5	$130.95	11.342%	$145.8023	$145.80	$145.80	$145.80
Purchase #6	$55.99	6.743%	$59.7654	$59.77	$59.75	$59.80
Purchase #7	$121.34	8.392%	$131.5229	$131.52	$131.50	$131.50
7 purchase totals =	$825.95		$908.6688	$908.67	$908.60	$908.70