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	$87.84	13.722%	$99.8934	$99.89	$99.90	$99.90
Purchase #2	$234.86	11.405%	$261.6458	$261.65	$261.65	$261.60
Purchase #3	$248.50	9.538%	$272.2019	$272.20	$272.20	$272.20
Purchase #4	$220.35	7.396%	$236.6471	$236.65	$236.65	$236.60
Purchase #5	$41.56	9.688%	$45.5863	$45.59	$45.60	$45.60
Purchase #6	$123.54	11.362%	$137.5766	$137.58	$137.60	$137.60
Purchase #7	$215.31	7.575%	$231.6197	$231.62	$231.60	$231.60
7 purchase totals =	$1,171.96		$1,285.1708	$1,285.18	$1,285.20	$1,285.10