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	$101.44	12.832%	$114.4568	$114.46	$114.45	$114.50
Purchase #2	$32.62	7.532%	$35.0769	$35.08	$35.10	$35.10
Purchase #3	$52.52	6.809%	$56.0961	$56.10	$56.10	$56.10
Purchase #4	$116.61	12.310%	$130.9647	$130.96	$130.95	$131.00
Purchase #5	$22.78	11.513%	$25.4027	$25.40	$25.40	$25.40
Purchase #6	$80.79	10.689%	$89.4256	$89.43	$89.45	$89.40
Purchase #7	$162.45	12.668%	$183.0292	$183.03	$183.05	$183.00
7 purchase totals =	$569.21		$634.4520	$634.46	$634.50	$634.50