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	$67.54	5.871%	$71.5053	$71.51	$71.50	$71.50
Purchase #2	$42.59	12.763%	$48.0258	$48.03	$48.05	$48.00
Purchase #3	$107.70	12.681%	$121.3574	$121.36	$121.35	$121.40
Purchase #4	$100.90	5.741%	$106.6927	$106.69	$106.70	$106.70
Purchase #5	$80.46	13.504%	$91.3253	$91.33	$91.35	$91.30
Purchase #6	$112.52	9.821%	$123.5706	$123.57	$123.55	$123.60
Purchase #7	$50.27	5.863%	$53.2173	$53.22	$53.20	$53.20
7 purchase totals =	$561.98		$615.6944	$615.71	$615.70	$615.70