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	$83.83	6.294%	$89.1063	$89.11	$89.10	$89.10
Purchase #2	$188.40	5.714%	$199.1652	$199.17	$199.15	$199.20
Purchase #3	$96.30	13.557%	$109.3554	$109.36	$109.35	$109.40
Purchase #4	$50.47	11.458%	$56.2529	$56.25	$56.25	$56.30
Purchase #5	$49.56	7.747%	$53.3994	$53.40	$53.40	$53.40
Purchase #6	$223.58	8.832%	$243.3266	$243.33	$243.35	$243.30
Purchase #7	$99.47	12.184%	$111.5894	$111.59	$111.60	$111.60
7 purchase totals =	$791.61		$862.1952	$862.21	$862.20	$862.30