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	$71.86	12.514%	$80.8526	$80.85	$80.85	$80.90
Purchase #2	$249.78	9.769%	$274.181	$274.18	$274.20	$274.20
Purchase #3	$195.74	4.659%	$204.8595	$204.86	$204.85	$204.90
Purchase #4	$80.25	6.627%	$85.5682	$85.57	$85.55	$85.60
Purchase #5	$164.76	5.553%	$173.9091	$173.91	$173.90	$173.90
Purchase #6	$172.91	9.136%	$188.7071	$188.71	$188.70	$188.70
Purchase #7	$88.53	4.516%	$92.528	$92.53	$92.55	$92.50
7 purchase totals =	$1,023.83		$1,100.6055	$1,100.61	$1,100.60	$1,100.70