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	$81.80	10.121%	$90.079	$90.08	$90.10	$90.10
Purchase #2	$173.78	10.327%	$191.7263	$191.73	$191.75	$191.70
Purchase #3	$89.96	5.230%	$94.6649	$94.66	$94.65	$94.70
Purchase #4	$212.66	6.204%	$225.8534	$225.85	$225.85	$225.90
Purchase #5	$201.38	13.194%	$227.9501	$227.95	$227.95	$228.00
Purchase #6	$73.60	6.324%	$78.2545	$78.25	$78.25	$78.30
Purchase #7	$181.38	10.223%	$199.9225	$199.92	$199.90	$199.90
7 purchase totals =	$1,014.56		$1,108.4507	$1,108.44	$1,108.45	$1,108.60