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	$74.39	13.132%	$84.1589	$84.16	$84.15	$84.20
Purchase #2	$200.98	11.861%	$224.8182	$224.82	$224.80	$224.80
Purchase #3	$183.82	3.670%	$190.5662	$190.57	$190.55	$190.60
Purchase #4	$165.58	3.630%	$171.5906	$171.59	$171.60	$171.60
Purchase #5	$132.90	13.874%	$151.3385	$151.34	$151.35	$151.30
Purchase #6	$50.29	10.686%	$55.664	$55.66	$55.65	$55.70
Purchase #7	$177.83	10.539%	$196.5715	$196.57	$196.55	$196.60
7 purchase totals =	$985.79		$1,074.7079	$1,074.71	$1,074.65	$1,074.80