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	$111.43	11.703%	$124.4707	$124.47	$124.45	$124.50
Purchase #2	$192.73	13.784%	$219.2959	$219.30	$219.30	$219.30
Purchase #3	$106.76	11.708%	$119.2595	$119.26	$119.25	$119.30
Purchase #4	$86.25	3.241%	$89.0454	$89.05	$89.05	$89.00
Purchase #5	$68.35	6.172%	$72.5686	$72.57	$72.55	$72.60
Purchase #6	$247.39	7.567%	$266.11	$266.11	$266.10	$266.10
Purchase #7	$44.56	12.347%	$50.0618	$50.06	$50.05	$50.10
7 purchase totals =	$857.47		$940.8119	$940.82	$940.75	$940.90