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	$92.96	7.747%	$100.1616	$100.16	$100.15	$100.20
Purchase #2	$16.46	12.300%	$18.4846	$18.48	$18.50	$18.50
Purchase #3	$105.30	12.426%	$118.3846	$118.38	$118.40	$118.40
Purchase #4	$31.47	12.692%	$35.4642	$35.46	$35.45	$35.50
Purchase #5	$160.53	6.850%	$171.5263	$171.53	$171.55	$171.50
Purchase #6	$221.76	4.123%	$230.9032	$230.90	$230.90	$230.90
Purchase #7	$147.40	12.652%	$166.049	$166.05	$166.05	$166.00
7 purchase totals =	$775.88		$840.9735	$840.96	$841.00	$841.00