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	$100.45	5.805%	$106.2811	$106.28	$106.30	$106.30
Purchase #2	$129.81	9.795%	$142.5249	$142.52	$142.50	$142.50
Purchase #3	$179.41	13.364%	$203.3864	$203.39	$203.40	$203.40
Purchase #4	$152.48	13.621%	$173.2493	$173.25	$173.25	$173.20
Purchase #5	$72.28	8.616%	$78.5076	$78.51	$78.50	$78.50
Purchase #6	$128.86	12.216%	$144.6015	$144.60	$144.60	$144.60
Purchase #7	$93.98	11.460%	$104.7501	$104.75	$104.75	$104.80
7 purchase totals =	$857.27		$953.3009	$953.30	$953.30	$953.30