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	$87.76	12.321%	$98.5729	$98.57	$98.55	$98.60
Purchase #2	$29.47	10.229%	$32.4845	$32.48	$32.50	$32.50
Purchase #3	$47.56	12.245%	$53.3837	$53.38	$53.40	$53.40
Purchase #4	$6.81	8.831%	$7.4114	$7.41	$7.40	$7.40
Purchase #5	$200.46	3.793%	$208.0634	$208.06	$208.05	$208.10
Purchase #6	$88.62	4.485%	$92.5946	$92.59	$92.60	$92.60
Purchase #7	$53.53	11.296%	$59.5767	$59.58	$59.60	$59.60
7 purchase totals =	$514.21		$552.0872	$552.07	$552.10	$552.20