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	$226.76	11.252%	$252.275	$252.28	$252.30	$252.30
Purchase #2	$181.25	3.372%	$187.3618	$187.36	$187.35	$187.40
Purchase #3	$175.57	9.548%	$192.3334	$192.33	$192.35	$192.30
Purchase #4	$82.59	8.502%	$89.6118	$89.61	$89.60	$89.60
Purchase #5	$95.76	4.761%	$100.3191	$100.32	$100.30	$100.30
Purchase #6	$130.60	9.120%	$142.5107	$142.51	$142.50	$142.50
Purchase #7	$220.35	11.482%	$245.6506	$245.65	$245.65	$245.70
7 purchase totals =	$1,112.88		$1,210.0624	$1,210.06	$1,210.05	$1,210.10