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	$70.36	6.432%	$74.8856	$74.89	$74.90	$74.90
Purchase #2	$37.28	7.667%	$40.1383	$40.14	$40.15	$40.10
Purchase #3	$36.47	10.589%	$40.3318	$40.33	$40.35	$40.30
Purchase #4	$27.56	4.841%	$28.8942	$28.89	$28.90	$28.90
Purchase #5	$85.95	12.693%	$96.8596	$96.86	$96.85	$96.90
Purchase #6	$93.69	12.622%	$105.5156	$105.52	$105.50	$105.50
Purchase #7	$53.88	3.546%	$55.7906	$55.79	$55.80	$55.80
7 purchase totals =	$405.19		$442.4157	$442.42	$442.45	$442.40