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	$26.51	5.589%	$27.9916	$27.99	$28.00	$28.00
Purchase #2	$171.85	11.515%	$191.6385	$191.64	$191.65	$191.60
Purchase #3	$100.91	3.612%	$104.5549	$104.55	$104.55	$104.60
Purchase #4	$230.91	4.754%	$241.8875	$241.89	$241.90	$241.90
Purchase #5	$27.98	3.185%	$28.8712	$28.87	$28.85	$28.90
Purchase #6	$128.74	10.771%	$142.6066	$142.61	$142.60	$142.60
Purchase #7	$174.67	6.418%	$185.8803	$185.88	$185.90	$185.90
7 purchase totals =	$861.57		$923.4306	$923.43	$923.45	$923.50