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	$117.55	5.775%	$124.3385	$124.34	$124.35	$124.30
Purchase #2	$36.78	3.606%	$38.1063	$38.11	$38.10	$38.10
Purchase #3	$35.70	8.311%	$38.667	$38.67	$38.65	$38.70
Purchase #4	$117.42	6.248%	$124.7564	$124.76	$124.75	$124.80
Purchase #5	$159.72	7.712%	$172.0376	$172.04	$172.05	$172.00
Purchase #6	$90.52	9.714%	$99.3131	$99.31	$99.30	$99.30
Purchase #7	$123.90	10.165%	$136.4944	$136.49	$136.50	$136.50
7 purchase totals =	$681.59		$733.7133	$733.72	$733.70	$733.70