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	$30.89	7.173%	$33.1057	$33.11	$33.10	$33.10
Purchase #2	$161.83	4.116%	$168.4909	$168.49	$168.50	$168.50
Purchase #3	$249.50	6.854%	$266.6007	$266.60	$266.60	$266.60
Purchase #4	$119.27	11.827%	$133.3761	$133.38	$133.40	$133.40
Purchase #5	$116.35	13.371%	$131.9072	$131.91	$131.90	$131.90
Purchase #6	$134.83	9.626%	$147.8087	$147.81	$147.80	$147.80
Purchase #7	$180.45	7.130%	$193.3161	$193.32	$193.30	$193.30
7 purchase totals =	$993.12		$1,074.6054	$1,074.62	$1,074.60	$1,074.60