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	$40.51	12.676%	$45.645	$45.65	$45.65	$45.60
Purchase #2	$35.88	4.560%	$37.5161	$37.52	$37.50	$37.50
Purchase #3	$81.67	9.663%	$89.5618	$89.56	$89.55	$89.60
Purchase #4	$61.80	11.550%	$68.9379	$68.94	$68.95	$68.90
Purchase #5	$127.28	12.750%	$143.5082	$143.51	$143.50	$143.50
Purchase #6	$200.50	11.454%	$223.4653	$223.47	$223.45	$223.50
Purchase #7	$204.66	6.608%	$218.1839	$218.18	$218.20	$218.20
7 purchase totals =	$752.30		$826.8182	$826.83	$826.80	$826.80