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	$80.25	12.874%	$90.5814	$90.58	$90.60	$90.60
Purchase #2	$214.39	10.347%	$236.5729	$236.57	$236.55	$236.60
Purchase #3	$169.88	6.467%	$180.8661	$180.87	$180.85	$180.90
Purchase #4	$39.96	11.227%	$44.4463	$44.45	$44.45	$44.40
Purchase #5	$56.53	5.500%	$59.6392	$59.64	$59.65	$59.60
Purchase #6	$162.35	6.591%	$173.0505	$173.05	$173.05	$173.10
Purchase #7	$148.69	7.454%	$159.7734	$159.77	$159.75	$159.80
7 purchase totals =	$872.05		$944.9298	$944.93	$944.90	$945.00