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	$19.41	6.423%	$20.6567	$20.66	$20.65	$20.70
Purchase #2	$69.40	6.514%	$73.9207	$73.92	$73.90	$73.90
Purchase #3	$203.74	4.491%	$212.89	$212.89	$212.90	$212.90
Purchase #4	$84.79	13.571%	$96.2969	$96.30	$96.30	$96.30
Purchase #5	$144.50	4.293%	$150.7034	$150.70	$150.70	$150.70
Purchase #6	$143.41	13.466%	$162.7216	$162.72	$162.70	$162.70
Purchase #7	$104.85	6.553%	$111.7208	$111.72	$111.70	$111.70
7 purchase totals =	$770.10		$828.9101	$828.91	$828.85	$828.90