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	$192.49	12.810%	$217.148	$217.15	$217.15	$217.10
Purchase #2	$245.43	13.390%	$278.2931	$278.29	$278.30	$278.30
Purchase #3	$218.29	4.787%	$228.7395	$228.74	$228.75	$228.70
Purchase #4	$48.93	5.624%	$51.6818	$51.68	$51.70	$51.70
Purchase #5	$91.90	9.437%	$100.5726	$100.57	$100.55	$100.60
Purchase #6	$27.43	3.561%	$28.4068	$28.41	$28.40	$28.40
Purchase #7	$93.25	5.523%	$98.4002	$98.40	$98.40	$98.40
7 purchase totals =	$917.72		$1,003.2420	$1,003.24	$1,003.25	$1,003.20