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	$131.75	9.400%	$144.1345	$144.13	$144.15	$144.10
Purchase #2	$209.36	7.735%	$225.554	$225.55	$225.55	$225.60
Purchase #3	$92.35	8.844%	$100.5174	$100.52	$100.50	$100.50
Purchase #4	$161.90	4.277%	$168.8245	$168.82	$168.80	$168.80
Purchase #5	$53.49	3.854%	$55.5515	$55.55	$55.55	$55.60
Purchase #6	$93.78	5.701%	$99.1264	$99.13	$99.15	$99.10
Purchase #7	$82.40	9.803%	$90.4777	$90.48	$90.50	$90.50
7 purchase totals =	$825.03		$884.1860	$884.18	$884.20	$884.20