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	$173.74	4.510%	$181.5757	$181.58	$181.60	$181.60
Purchase #2	$24.43	13.483%	$27.7239	$27.72	$27.70	$27.70
Purchase #3	$195.76	5.549%	$206.6227	$206.62	$206.60	$206.60
Purchase #4	$59.57	12.790%	$67.189	$67.19	$67.20	$67.20
Purchase #5	$222.95	12.303%	$250.3795	$250.38	$250.40	$250.40
Purchase #6	$82.49	10.107%	$90.8273	$90.83	$90.85	$90.80
Purchase #7	$53.43	9.557%	$58.5363	$58.54	$58.55	$58.50
7 purchase totals =	$812.37		$882.8544	$882.86	$882.90	$882.80