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	$93.78	5.611%	$99.042	$99.04	$99.05	$99.00
Purchase #2	$125.47	8.809%	$136.5227	$136.52	$136.50	$136.50
Purchase #3	$187.85	8.671%	$204.1385	$204.14	$204.15	$204.10
Purchase #4	$110.89	6.312%	$117.8894	$117.89	$117.90	$117.90
Purchase #5	$144.78	5.377%	$152.5648	$152.56	$152.55	$152.60
Purchase #6	$215.92	6.765%	$230.527	$230.53	$230.55	$230.50
Purchase #7	$221.31	9.764%	$242.9187	$242.92	$242.90	$242.90
7 purchase totals =	$1,100.00		$1,183.6031	$1,183.60	$1,183.60	$1,183.50