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	$127.62	11.319%	$142.0653	$142.07	$142.05	$142.10
Purchase #2	$51.41	8.139%	$55.5943	$55.59	$55.60	$55.60
Purchase #3	$207.45	7.797%	$223.6249	$223.62	$223.60	$223.60
Purchase #4	$54.75	8.261%	$59.2729	$59.27	$59.25	$59.30
Purchase #5	$118.66	9.145%	$129.5115	$129.51	$129.50	$129.50
Purchase #6	$34.77	3.163%	$35.8698	$35.87	$35.85	$35.90
Purchase #7	$108.37	13.546%	$123.0498	$123.05	$123.05	$123.00
7 purchase totals =	$703.03		$768.9885	$768.98	$768.90	$769.00