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	$49.31	3.220%	$50.8978	$50.90	$50.90	$50.90
Purchase #2	$116.71	12.687%	$131.517	$131.52	$131.50	$131.50
Purchase #3	$45.57	8.290%	$49.3478	$49.35	$49.35	$49.30
Purchase #4	$92.82	3.728%	$96.2803	$96.28	$96.30	$96.30
Purchase #5	$62.69	13.607%	$71.2202	$71.22	$71.20	$71.20
Purchase #6	$31.60	3.604%	$32.7389	$32.74	$32.75	$32.70
Purchase #7	$188.31	5.832%	$199.2922	$199.29	$199.30	$199.30
7 purchase totals =	$587.01		$631.2942	$631.30	$631.30	$631.20