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	$34.42	9.582%	$37.7181	$37.72	$37.70	$37.70
Purchase #2	$229.58	8.298%	$248.6305	$248.63	$248.65	$248.60
Purchase #3	$118.71	10.631%	$131.3301	$131.33	$131.35	$131.30
Purchase #4	$88.35	12.414%	$99.3178	$99.32	$99.30	$99.30
Purchase #5	$161.96	4.109%	$168.6149	$168.61	$168.60	$168.60
Purchase #6	$28.60	13.485%	$32.4567	$32.46	$32.45	$32.50
Purchase #7	$125.56	11.766%	$140.3334	$140.33	$140.35	$140.30
7 purchase totals =	$787.18		$858.4015	$858.40	$858.40	$858.30