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	$191.90	12.831%	$216.5227	$216.52	$216.50	$216.50
Purchase #2	$138.32	12.722%	$155.9171	$155.92	$155.90	$155.90
Purchase #3	$119.93	7.407%	$128.8132	$128.81	$128.80	$128.80
Purchase #4	$77.91	6.331%	$82.8425	$82.84	$82.85	$82.80
Purchase #5	$105.68	5.201%	$111.1764	$111.18	$111.20	$111.20
Purchase #6	$16.42	6.457%	$17.4802	$17.48	$17.50	$17.50
Purchase #7	$141.37	5.695%	$149.421	$149.42	$149.40	$149.40
7 purchase totals =	$791.53		$862.1731	$862.17	$862.15	$862.10