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	$76.50	9.473%	$83.7468	$83.75	$83.75	$83.70
Purchase #2	$93.50	6.303%	$99.3933	$99.39	$99.40	$99.40
Purchase #3	$127.36	9.488%	$139.4439	$139.44	$139.45	$139.40
Purchase #4	$48.58	8.421%	$52.6709	$52.67	$52.65	$52.70
Purchase #5	$28.53	12.177%	$32.0041	$32.00	$32.00	$32.00
Purchase #6	$96.52	13.403%	$109.4566	$109.46	$109.45	$109.50
Purchase #7	$147.98	12.403%	$166.334	$166.33	$166.35	$166.30
7 purchase totals =	$618.97		$683.0496	$683.04	$683.05	$683.00