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	$244.94	10.687%	$271.1167	$271.12	$271.10	$271.10
Purchase #2	$82.38	8.234%	$89.1632	$89.16	$89.15	$89.20
Purchase #3	$247.86	8.259%	$268.3308	$268.33	$268.35	$268.30
Purchase #4	$7.50	4.671%	$7.8503	$7.85	$7.85	$7.90
Purchase #5	$166.39	8.469%	$180.4816	$180.48	$180.50	$180.50
Purchase #6	$100.45	9.735%	$110.2288	$110.23	$110.25	$110.20
Purchase #7	$189.88	10.333%	$209.5003	$209.50	$209.50	$209.50
7 purchase totals =	$1,039.40		$1,136.6717	$1,136.67	$1,136.70	$1,136.70