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	$242.30	3.195%	$250.0415	$250.04	$250.05	$250.00
Purchase #2	$67.76	13.174%	$76.6867	$76.69	$76.70	$76.70
Purchase #3	$233.55	4.855%	$244.8889	$244.89	$244.90	$244.90
Purchase #4	$229.67	11.145%	$255.2667	$255.27	$255.25	$255.30
Purchase #5	$45.54	4.520%	$47.5984	$47.60	$47.60	$47.60
Purchase #6	$53.88	4.240%	$56.1645	$56.16	$56.15	$56.20
Purchase #7	$77.40	7.280%	$83.0347	$83.03	$83.05	$83.00
7 purchase totals =	$950.10		$1,013.6814	$1,013.68	$1,013.70	$1,013.70