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	$135.84	6.295%	$144.3911	$144.39	$144.40	$144.40
Purchase #2	$181.59	5.510%	$191.5956	$191.60	$191.60	$191.60
Purchase #3	$249.58	10.672%	$276.2152	$276.22	$276.20	$276.20
Purchase #4	$60.43	6.176%	$64.1622	$64.16	$64.15	$64.20
Purchase #5	$211.71	5.515%	$223.3858	$223.39	$223.40	$223.40
Purchase #6	$173.33	13.601%	$196.9046	$196.90	$196.90	$196.90
Purchase #7	$129.54	6.327%	$137.736	$137.74	$137.75	$137.70
7 purchase totals =	$1,142.02		$1,234.3905	$1,234.40	$1,234.40	$1,234.40