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	$134.29	12.531%	$151.1179	$151.12	$151.10	$151.10
Purchase #2	$96.48	4.217%	$100.5486	$100.55	$100.55	$100.50
Purchase #3	$198.63	13.644%	$225.7311	$225.73	$225.75	$225.70
Purchase #4	$69.98	10.430%	$77.2789	$77.28	$77.30	$77.30
Purchase #5	$97.50	12.742%	$109.9235	$109.92	$109.90	$109.90
Purchase #6	$49.57	13.546%	$56.2848	$56.28	$56.30	$56.30
Purchase #7	$241.57	3.464%	$249.938	$249.94	$249.95	$249.90
7 purchase totals =	$888.02		$970.8228	$970.82	$970.85	$970.70