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	$71.78	8.798%	$78.0952	$78.10	$78.10	$78.10
Purchase #2	$217.61	13.556%	$247.1092	$247.11	$247.10	$247.10
Purchase #3	$173.79	7.329%	$186.5271	$186.53	$186.55	$186.50
Purchase #4	$120.69	13.715%	$137.2426	$137.24	$137.25	$137.20
Purchase #5	$73.59	5.154%	$77.3828	$77.38	$77.40	$77.40
Purchase #6	$109.52	8.231%	$118.5346	$118.53	$118.55	$118.50
Purchase #7	$31.64	5.313%	$33.321	$33.32	$33.30	$33.30
7 purchase totals =	$798.62		$878.2125	$878.21	$878.25	$878.10