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	$250.79	6.775%	$267.781	$267.78	$267.80	$267.80
Purchase #2	$151.37	4.129%	$157.6201	$157.62	$157.60	$157.60
Purchase #3	$54.55	9.198%	$59.5675	$59.57	$59.55	$59.60
Purchase #4	$130.99	12.125%	$146.8725	$146.87	$146.85	$146.90
Purchase #5	$41.41	9.172%	$45.2081	$45.21	$45.20	$45.20
Purchase #6	$92.69	7.703%	$99.8299	$99.83	$99.85	$99.80
Purchase #7	$44.70	12.361%	$50.2254	$50.23	$50.25	$50.20
7 purchase totals =	$766.50		$827.1045	$827.11	$827.10	$827.10