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	$90.42	10.512%	$99.925	$99.93	$99.95	$99.90
Purchase #2	$5.43	13.225%	$6.1481	$6.15	$6.15	$6.10
Purchase #3	$103.88	5.431%	$109.5217	$109.52	$109.50	$109.50
Purchase #4	$246.63	4.162%	$256.8947	$256.89	$256.90	$256.90
Purchase #5	$68.47	4.195%	$71.3423	$71.34	$71.35	$71.30
Purchase #6	$133.99	6.502%	$142.702	$142.70	$142.70	$142.70
Purchase #7	$46.26	8.669%	$50.2703	$50.27	$50.25	$50.30
7 purchase totals =	$695.08		$736.8041	$736.80	$736.80	$736.70