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	$246.83	9.164%	$269.4495	$269.45	$269.45	$269.40
Purchase #2	$69.96	8.500%	$75.9066	$75.91	$75.90	$75.90
Purchase #3	$182.59	4.152%	$190.1711	$190.17	$190.15	$190.20
Purchase #4	$140.50	7.298%	$150.7537	$150.75	$150.75	$150.80
Purchase #5	$236.87	6.340%	$251.8876	$251.89	$251.90	$251.90
Purchase #6	$233.27	4.618%	$244.0424	$244.04	$244.05	$244.00
Purchase #7	$86.56	13.131%	$97.9262	$97.93	$97.95	$97.90
7 purchase totals =	$1,196.58		$1,280.1371	$1,280.14	$1,280.15	$1,280.10