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	$166.58	10.715%	$184.429	$184.43	$184.45	$184.40
Purchase #2	$99.42	11.437%	$110.7907	$110.79	$110.80	$110.80
Purchase #3	$28.86	11.228%	$32.1004	$32.10	$32.10	$32.10
Purchase #4	$88.48	12.711%	$99.7267	$99.73	$99.75	$99.70
Purchase #5	$20.88	8.309%	$22.6149	$22.61	$22.60	$22.60
Purchase #6	$89.44	7.334%	$95.9995	$96.00	$96.00	$96.00
Purchase #7	$40.68	4.414%	$42.4756	$42.48	$42.50	$42.50
7 purchase totals =	$534.34		$588.1368	$588.14	$588.20	$588.10