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	$48.27	10.531%	$53.3533	$53.35	$53.35	$53.40
Purchase #2	$159.33	11.420%	$177.5255	$177.53	$177.55	$177.50
Purchase #3	$83.88	13.495%	$95.1996	$95.20	$95.20	$95.20
Purchase #4	$37.37	12.711%	$42.1201	$42.12	$42.10	$42.10
Purchase #5	$201.87	10.611%	$223.2904	$223.29	$223.30	$223.30
Purchase #6	$134.63	6.614%	$143.5344	$143.53	$143.55	$143.50
Purchase #7	$56.92	11.112%	$63.245	$63.25	$63.25	$63.20
7 purchase totals =	$722.27		$798.2683	$798.27	$798.30	$798.20