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	$239.71	10.262%	$264.309	$264.31	$264.30	$264.30
Purchase #2	$100.71	8.375%	$109.1445	$109.14	$109.15	$109.10
Purchase #3	$74.34	5.541%	$78.4592	$78.46	$78.45	$78.50
Purchase #4	$204.87	5.603%	$216.3489	$216.35	$216.35	$216.30
Purchase #5	$79.45	10.198%	$87.5523	$87.55	$87.55	$87.60
Purchase #6	$63.36	7.156%	$67.894	$67.89	$67.90	$67.90
Purchase #7	$83.38	5.157%	$87.6799	$87.68	$87.70	$87.70
7 purchase totals =	$845.82		$911.3878	$911.38	$911.40	$911.40