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	$70.32	11.535%	$78.4314	$78.43	$78.45	$78.40
Purchase #2	$54.61	4.335%	$56.9773	$56.98	$57.00	$57.00
Purchase #3	$247.40	4.756%	$259.1663	$259.17	$259.15	$259.20
Purchase #4	$240.75	3.194%	$248.4396	$248.44	$248.45	$248.40
Purchase #5	$56.62	9.294%	$61.8823	$61.88	$61.90	$61.90
Purchase #6	$35.27	9.647%	$38.6725	$38.67	$38.65	$38.70
Purchase #7	$67.37	3.744%	$69.8923	$69.89	$69.90	$69.90
7 purchase totals =	$772.34		$813.4617	$813.46	$813.50	$813.50