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	$71.61	9.421%	$78.3564	$78.36	$78.35	$78.40
Purchase #2	$189.47	5.510%	$199.9098	$199.91	$199.90	$199.90
Purchase #3	$107.59	4.189%	$112.0969	$112.10	$112.10	$112.10
Purchase #4	$172.72	7.200%	$185.1558	$185.16	$185.15	$185.20
Purchase #5	$34.47	7.750%	$37.1414	$37.14	$37.15	$37.10
Purchase #6	$135.37	7.761%	$145.8761	$145.88	$145.90	$145.90
Purchase #7	$221.84	5.773%	$234.6468	$234.65	$234.65	$234.60
7 purchase totals =	$933.07		$993.1832	$993.20	$993.20	$993.20