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	$52.94	11.180%	$58.8587	$58.86	$58.85	$58.90
Purchase #2	$234.57	12.748%	$264.473	$264.47	$264.45	$264.50
Purchase #3	$233.64	5.865%	$247.343	$247.34	$247.35	$247.30
Purchase #4	$35.90	6.703%	$38.3064	$38.31	$38.30	$38.30
Purchase #5	$151.34	5.402%	$159.5154	$159.52	$159.50	$159.50
Purchase #6	$18.37	9.620%	$20.1372	$20.14	$20.15	$20.10
Purchase #7	$9.64	12.576%	$10.8523	$10.85	$10.85	$10.90
7 purchase totals =	$736.40		$799.4860	$799.49	$799.45	$799.50