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	$143.62	12.663%	$161.8066	$161.81	$161.80	$161.80
Purchase #2	$113.58	12.752%	$128.0637	$128.06	$128.05	$128.10
Purchase #3	$27.35	9.145%	$29.8512	$29.85	$29.85	$29.90
Purchase #4	$147.46	3.659%	$152.8556	$152.86	$152.85	$152.90
Purchase #5	$143.39	4.536%	$149.8942	$149.89	$149.90	$149.90
Purchase #6	$193.53	9.803%	$212.5017	$212.50	$212.50	$212.50
Purchase #7	$244.94	12.872%	$276.4687	$276.47	$276.45	$276.50
7 purchase totals =	$1,013.87		$1,111.4417	$1,111.44	$1,111.40	$1,111.60