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	$112.97	10.843%	$125.2193	$125.22	$125.20	$125.20
Purchase #2	$29.48	10.276%	$32.5094	$32.51	$32.50	$32.50
Purchase #3	$123.78	5.144%	$130.1472	$130.15	$130.15	$130.10
Purchase #4	$128.64	11.519%	$143.458	$143.46	$143.45	$143.50
Purchase #5	$165.36	4.298%	$172.4672	$172.47	$172.45	$172.50
Purchase #6	$188.42	7.295%	$202.1652	$202.17	$202.15	$202.20
Purchase #7	$166.86	4.522%	$174.4054	$174.41	$174.40	$174.40
7 purchase totals =	$915.51		$980.3717	$980.39	$980.30	$980.40