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	$137.93	13.490%	$156.5368	$156.54	$156.55	$156.50
Purchase #2	$131.35	6.298%	$139.6224	$139.62	$139.60	$139.60
Purchase #3	$81.99	9.277%	$89.5962	$89.60	$89.60	$89.60
Purchase #4	$125.36	4.172%	$130.59	$130.59	$130.60	$130.60
Purchase #5	$232.82	10.565%	$257.4174	$257.42	$257.40	$257.40
Purchase #6	$185.88	3.115%	$191.6702	$191.67	$191.65	$191.70
Purchase #7	$33.92	9.419%	$37.1149	$37.11	$37.10	$37.10
7 purchase totals =	$929.25		$1,002.5479	$1,002.55	$1,002.50	$1,002.50