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	$88.79	12.710%	$100.0752	$100.08	$100.10	$100.10
Purchase #2	$107.59	4.208%	$112.1174	$112.12	$112.10	$112.10
Purchase #3	$64.82	10.282%	$71.4848	$71.48	$71.50	$71.50
Purchase #4	$206.36	6.213%	$219.1811	$219.18	$219.20	$219.20
Purchase #5	$92.26	5.699%	$97.5179	$97.52	$97.50	$97.50
Purchase #6	$109.95	7.435%	$118.1248	$118.12	$118.10	$118.10
Purchase #7	$136.82	3.596%	$141.74	$141.74	$141.75	$141.70
7 purchase totals =	$806.59		$860.2412	$860.24	$860.25	$860.20