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	$129.32	7.144%	$138.5586	$138.56	$138.55	$138.60
Purchase #2	$116.32	9.249%	$127.0784	$127.08	$127.10	$127.10
Purchase #3	$190.89	4.617%	$199.7034	$199.70	$199.70	$199.70
Purchase #4	$235.64	8.869%	$256.5389	$256.54	$256.55	$256.50
Purchase #5	$5.62	6.840%	$6.0044	$6.00	$6.00	$6.00
Purchase #6	$204.28	9.618%	$223.9277	$223.93	$223.95	$223.90
Purchase #7	$139.43	6.805%	$148.9182	$148.92	$148.90	$148.90
7 purchase totals =	$1,021.50		$1,100.7296	$1,100.73	$1,100.75	$1,100.70