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	$17.44	3.850%	$18.1114	$18.11	$18.10	$18.10
Purchase #2	$162.45	3.467%	$168.0821	$168.08	$168.10	$168.10
Purchase #3	$74.45	11.406%	$82.9418	$82.94	$82.95	$82.90
Purchase #4	$52.79	13.197%	$59.7567	$59.76	$59.75	$59.80
Purchase #5	$230.37	12.314%	$258.7378	$258.74	$258.75	$258.70
Purchase #6	$247.58	8.454%	$268.5104	$268.51	$268.50	$268.50
Purchase #7	$106.78	9.401%	$116.8184	$116.82	$116.80	$116.80
7 purchase totals =	$891.86		$972.9586	$972.96	$972.95	$972.90