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	$136.51	12.632%	$153.7539	$153.75	$153.75	$153.80
Purchase #2	$64.74	8.598%	$70.3063	$70.31	$70.30	$70.30
Purchase #3	$75.93	12.427%	$85.3658	$85.37	$85.35	$85.40
Purchase #4	$94.72	11.205%	$105.3334	$105.33	$105.35	$105.30
Purchase #5	$182.43	8.280%	$197.5352	$197.54	$197.55	$197.50
Purchase #6	$77.89	9.243%	$85.0894	$85.09	$85.10	$85.10
Purchase #7	$83.90	13.275%	$95.0377	$95.04	$95.05	$95.00
7 purchase totals =	$716.12		$792.4217	$792.43	$792.45	$792.40