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	$90.41	6.524%	$96.3083	$96.31	$96.30	$96.30
Purchase #2	$87.40	3.767%	$90.6924	$90.69	$90.70	$90.70
Purchase #3	$99.66	9.801%	$109.4277	$109.43	$109.45	$109.40
Purchase #4	$151.55	9.684%	$166.2261	$166.23	$166.25	$166.20
Purchase #5	$118.49	4.763%	$124.1337	$124.13	$124.15	$124.10
Purchase #6	$180.82	12.114%	$202.7245	$202.72	$202.70	$202.70
Purchase #7	$43.42	5.738%	$45.9114	$45.91	$45.90	$45.90
7 purchase totals =	$771.75		$835.4241	$835.42	$835.45	$835.30