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	$250.63	12.802%	$282.7157	$282.72	$282.70	$282.70
Purchase #2	$60.64	12.670%	$68.3231	$68.32	$68.30	$68.30
Purchase #3	$216.75	9.642%	$237.649	$237.65	$237.65	$237.60
Purchase #4	$17.33	7.549%	$18.6382	$18.64	$18.65	$18.60
Purchase #5	$76.83	11.405%	$85.5925	$85.59	$85.60	$85.60
Purchase #6	$89.67	12.170%	$100.5828	$100.58	$100.60	$100.60
Purchase #7	$145.33	3.308%	$150.1375	$150.14	$150.15	$150.10
7 purchase totals =	$857.18		$943.6388	$943.64	$943.65	$943.50