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	$23.99	12.656%	$27.0262	$27.03	$27.05	$27.00
Purchase #2	$40.96	4.276%	$42.7114	$42.71	$42.70	$42.70
Purchase #3	$175.34	4.714%	$183.6055	$183.61	$183.60	$183.60
Purchase #4	$130.36	10.762%	$144.3893	$144.39	$144.40	$144.40
Purchase #5	$90.60	11.240%	$100.7834	$100.78	$100.80	$100.80
Purchase #6	$248.82	5.872%	$263.4307	$263.43	$263.45	$263.40
Purchase #7	$245.79	10.774%	$272.2714	$272.27	$272.25	$272.30
7 purchase totals =	$955.86		$1,034.2179	$1,034.22	$1,034.25	$1,034.20