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	$160.85	6.507%	$171.3165	$171.32	$171.30	$171.30
Purchase #2	$33.38	11.296%	$37.1506	$37.15	$37.15	$37.20
Purchase #3	$211.48	10.497%	$233.6791	$233.68	$233.70	$233.70
Purchase #4	$145.78	12.346%	$163.778	$163.78	$163.80	$163.80
Purchase #5	$18.27	3.236%	$18.8612	$18.86	$18.85	$18.90
Purchase #6	$94.43	10.624%	$104.4622	$104.46	$104.45	$104.50
Purchase #7	$95.54	3.621%	$98.9995	$99.00	$99.00	$99.00
7 purchase totals =	$759.73		$828.2471	$828.25	$828.25	$828.40