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	$19.93	6.117%	$21.1491	$21.15	$21.15	$21.10
Purchase #2	$175.64	3.464%	$181.7242	$181.72	$181.70	$181.70
Purchase #3	$184.33	3.423%	$190.6396	$190.64	$190.65	$190.60
Purchase #4	$209.99	7.230%	$225.1723	$225.17	$225.15	$225.20
Purchase #5	$230.53	3.282%	$238.096	$238.10	$238.10	$238.10
Purchase #6	$38.78	9.698%	$42.5409	$42.54	$42.55	$42.50
Purchase #7	$49.34	9.397%	$53.9765	$53.98	$54.00	$54.00
7 purchase totals =	$908.54		$953.2986	$953.30	$953.30	$953.20