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	$203.49	12.594%	$229.1175	$229.12	$229.10	$229.10
Purchase #2	$87.53	13.699%	$99.5207	$99.52	$99.50	$99.50
Purchase #3	$58.83	10.233%	$64.8501	$64.85	$64.85	$64.90
Purchase #4	$247.30	12.369%	$277.8885	$277.89	$277.90	$277.90
Purchase #5	$154.31	13.684%	$175.4258	$175.43	$175.45	$175.40
Purchase #6	$67.25	4.408%	$70.2144	$70.21	$70.20	$70.20
Purchase #7	$58.86	5.759%	$62.2497	$62.25	$62.25	$62.20
7 purchase totals =	$877.57		$979.2667	$979.27	$979.25	$979.20