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	$85.70	4.417%	$89.4854	$89.49	$89.50	$89.50
Purchase #2	$49.33	6.674%	$52.6223	$52.62	$52.60	$52.60
Purchase #3	$223.67	10.635%	$247.4573	$247.46	$247.45	$247.50
Purchase #4	$64.75	6.420%	$68.907	$68.91	$68.90	$68.90
Purchase #5	$168.98	8.233%	$182.8921	$182.89	$182.90	$182.90
Purchase #6	$60.64	5.586%	$64.0274	$64.03	$64.05	$64.00
Purchase #7	$150.60	10.408%	$166.2744	$166.27	$166.25	$166.30
7 purchase totals =	$803.67		$871.6659	$871.67	$871.65	$871.70