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	$228.44	13.327%	$258.8842	$258.88	$258.90	$258.90
Purchase #2	$234.43	9.165%	$255.9155	$255.92	$255.90	$255.90
Purchase #3	$153.38	13.326%	$173.8194	$173.82	$173.80	$173.80
Purchase #4	$98.54	4.293%	$102.7703	$102.77	$102.75	$102.80
Purchase #5	$114.63	9.410%	$125.4167	$125.42	$125.40	$125.40
Purchase #6	$70.57	11.799%	$78.8966	$78.90	$78.90	$78.90
Purchase #7	$48.56	12.154%	$54.462	$54.46	$54.45	$54.50
7 purchase totals =	$948.55		$1,050.1647	$1,050.17	$1,050.10	$1,050.20