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	$168.31	12.604%	$189.5238	$189.52	$189.50	$189.50
Purchase #2	$230.98	4.309%	$240.9329	$240.93	$240.95	$240.90
Purchase #3	$233.25	13.381%	$264.4612	$264.46	$264.45	$264.50
Purchase #4	$50.85	9.588%	$55.7255	$55.73	$55.75	$55.70
Purchase #5	$124.83	3.175%	$128.7934	$128.79	$128.80	$128.80
Purchase #6	$131.66	9.469%	$144.1269	$144.13	$144.15	$144.10
Purchase #7	$147.89	4.546%	$154.6131	$154.61	$154.60	$154.60
7 purchase totals =	$1,087.77		$1,178.1768	$1,178.17	$1,178.20	$1,178.10