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	$79.82	4.374%	$83.3113	$83.31	$83.30	$83.30
Purchase #2	$52.91	10.225%	$58.32	$58.32	$58.30	$58.30
Purchase #3	$101.86	7.669%	$109.6716	$109.67	$109.65	$109.70
Purchase #4	$100.40	8.469%	$108.9029	$108.90	$108.90	$108.90
Purchase #5	$183.39	9.207%	$200.2747	$200.27	$200.25	$200.30
Purchase #6	$28.85	10.514%	$31.8833	$31.88	$31.90	$31.90
Purchase #7	$141.42	9.762%	$155.2254	$155.23	$155.25	$155.20
7 purchase totals =	$688.65		$747.5892	$747.58	$747.55	$747.60