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	$101.89	9.393%	$111.4605	$111.46	$111.45	$111.50
Purchase #2	$150.45	8.107%	$162.647	$162.65	$162.65	$162.60
Purchase #3	$232.54	5.457%	$245.2297	$245.23	$245.25	$245.20
Purchase #4	$98.58	5.551%	$104.0522	$104.05	$104.05	$104.10
Purchase #5	$19.69	6.529%	$20.9756	$20.98	$21.00	$21.00
Purchase #6	$118.57	4.489%	$123.8926	$123.89	$123.90	$123.90
Purchase #7	$141.66	6.783%	$151.2688	$151.27	$151.25	$151.30
7 purchase totals =	$863.38		$919.5264	$919.53	$919.55	$919.60