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	$54.31	8.644%	$59.0046	$59.00	$59.00	$59.00
Purchase #2	$230.81	6.114%	$244.9217	$244.92	$244.90	$244.90
Purchase #3	$222.27	6.184%	$236.0152	$236.02	$236.00	$236.00
Purchase #4	$19.34	8.673%	$21.0174	$21.02	$21.00	$21.00
Purchase #5	$140.41	7.398%	$150.7975	$150.80	$150.80	$150.80
Purchase #6	$58.57	11.574%	$65.3489	$65.35	$65.35	$65.30
Purchase #7	$127.56	4.196%	$132.9124	$132.91	$132.90	$132.90
7 purchase totals =	$853.27		$910.0177	$910.02	$909.95	$909.90