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	$164.40	5.817%	$173.9631	$173.96	$173.95	$174.00
Purchase #2	$48.78	12.330%	$54.7946	$54.79	$54.80	$54.80
Purchase #3	$45.47	11.106%	$50.5199	$50.52	$50.50	$50.50
Purchase #4	$207.60	5.410%	$218.8312	$218.83	$218.85	$218.80
Purchase #5	$119.73	11.501%	$133.5001	$133.50	$133.50	$133.50
Purchase #6	$106.38	3.221%	$109.8065	$109.81	$109.80	$109.80
Purchase #7	$36.49	13.661%	$41.4749	$41.47	$41.45	$41.50
7 purchase totals =	$728.85		$782.8903	$782.88	$782.85	$782.90