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	$249.41	12.846%	$281.4492	$281.45	$281.45	$281.40
Purchase #2	$243.90	9.803%	$267.8095	$267.81	$267.80	$267.80
Purchase #3	$34.28	9.199%	$37.4334	$37.43	$37.45	$37.40
Purchase #4	$34.38	10.730%	$38.069	$38.07	$38.05	$38.10
Purchase #5	$223.28	5.761%	$236.1432	$236.14	$236.15	$236.10
Purchase #6	$125.80	9.632%	$137.9171	$137.92	$137.90	$137.90
Purchase #7	$57.83	8.407%	$62.6918	$62.69	$62.70	$62.70
7 purchase totals =	$968.88		$1,061.5132	$1,061.51	$1,061.50	$1,061.40