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	$34.41	11.222%	$38.2715	$38.27	$38.25	$38.30
Purchase #2	$72.84	13.131%	$82.4046	$82.40	$82.40	$82.40
Purchase #3	$245.99	10.401%	$271.5754	$271.58	$271.60	$271.60
Purchase #4	$83.72	7.767%	$90.2225	$90.22	$90.20	$90.20
Purchase #5	$5.57	10.791%	$6.1711	$6.17	$6.15	$6.20
Purchase #6	$7.34	6.245%	$7.7984	$7.80	$7.80	$7.80
Purchase #7	$175.37	6.564%	$186.8813	$186.88	$186.90	$186.90
7 purchase totals =	$625.24		$683.3248	$683.32	$683.30	$683.40