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	$29.32	10.109%	$32.284	$32.28	$32.30	$32.30
Purchase #2	$124.85	13.228%	$141.3652	$141.37	$141.35	$141.40
Purchase #3	$140.39	10.825%	$155.5872	$155.59	$155.60	$155.60
Purchase #4	$31.74	4.415%	$33.1413	$33.14	$33.15	$33.10
Purchase #5	$43.29	11.168%	$48.1246	$48.12	$48.10	$48.10
Purchase #6	$35.67	3.455%	$36.9024	$36.90	$36.90	$36.90
Purchase #7	$128.52	5.253%	$135.2712	$135.27	$135.25	$135.30
7 purchase totals =	$533.78		$582.6759	$582.67	$582.65	$582.70