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	$79.36	12.194%	$89.0372	$89.04	$89.05	$89.00
Purchase #2	$250.40	10.516%	$276.7321	$276.73	$276.75	$276.70
Purchase #3	$139.79	12.358%	$157.0652	$157.07	$157.05	$157.10
Purchase #4	$64.36	13.191%	$72.8497	$72.85	$72.85	$72.80
Purchase #5	$70.60	10.753%	$78.1916	$78.19	$78.20	$78.20
Purchase #6	$77.92	4.843%	$81.6937	$81.69	$81.70	$81.70
Purchase #7	$158.41	4.114%	$164.927	$164.93	$164.95	$164.90
7 purchase totals =	$840.84		$920.4965	$920.50	$920.55	$920.40