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	$79.54	13.229%	$90.0623	$90.06	$90.05	$90.10
Purchase #2	$37.93	11.676%	$42.3587	$42.36	$42.35	$42.40
Purchase #3	$44.62	4.234%	$46.5092	$46.51	$46.50	$46.50
Purchase #4	$224.58	12.864%	$253.47	$253.47	$253.45	$253.50
Purchase #5	$64.50	7.596%	$69.3994	$69.40	$69.40	$69.40
Purchase #6	$162.74	6.729%	$173.6908	$173.69	$173.70	$173.70
Purchase #7	$178.78	4.487%	$186.8019	$186.80	$186.80	$186.80
7 purchase totals =	$792.69		$862.2923	$862.29	$862.25	$862.40