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	$27.76	12.516%	$31.2344	$31.23	$31.25	$31.20
Purchase #2	$137.92	10.305%	$152.1327	$152.13	$152.15	$152.10
Purchase #3	$116.73	12.489%	$131.3084	$131.31	$131.30	$131.30
Purchase #4	$21.53	4.734%	$22.5492	$22.55	$22.55	$22.50
Purchase #5	$113.27	9.130%	$123.6116	$123.61	$123.60	$123.60
Purchase #6	$184.35	3.183%	$190.2179	$190.22	$190.20	$190.20
Purchase #7	$138.31	8.809%	$150.4937	$150.49	$150.50	$150.50
7 purchase totals =	$739.87		$801.5479	$801.54	$801.55	$801.40