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	$57.52	6.687%	$61.3664	$61.37	$61.35	$61.40
Purchase #2	$133.39	6.311%	$141.8082	$141.81	$141.80	$141.80
Purchase #3	$121.61	13.657%	$138.2183	$138.22	$138.20	$138.20
Purchase #4	$78.72	12.181%	$88.3089	$88.31	$88.30	$88.30
Purchase #5	$146.63	12.459%	$164.8986	$164.90	$164.90	$164.90
Purchase #6	$123.88	12.656%	$139.5583	$139.56	$139.55	$139.60
Purchase #7	$173.99	6.689%	$185.6282	$185.63	$185.65	$185.60
7 purchase totals =	$835.74		$919.7869	$919.80	$919.75	$919.80