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	$103.76	6.624%	$110.6331	$110.63	$110.65	$110.60
Purchase #2	$233.61	10.829%	$258.9076	$258.91	$258.90	$258.90
Purchase #3	$103.55	5.480%	$109.2245	$109.22	$109.20	$109.20
Purchase #4	$92.27	11.803%	$103.1606	$103.16	$103.15	$103.20
Purchase #5	$20.27	4.499%	$21.1819	$21.18	$21.20	$21.20
Purchase #6	$51.32	4.120%	$53.4344	$53.43	$53.45	$53.40
Purchase #7	$168.87	6.314%	$179.5325	$179.53	$179.55	$179.50
7 purchase totals =	$773.65		$836.0746	$836.06	$836.10	$836.00