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	$155.88	8.115%	$168.5297	$168.53	$168.55	$168.50
Purchase #2	$250.64	9.496%	$274.4408	$274.44	$274.45	$274.40
Purchase #3	$152.86	6.646%	$163.0191	$163.02	$163.00	$163.00
Purchase #4	$118.38	12.460%	$133.1301	$133.13	$133.15	$133.10
Purchase #5	$60.31	9.822%	$66.2336	$66.23	$66.25	$66.20
Purchase #6	$39.72	6.304%	$42.2239	$42.22	$42.20	$42.20
Purchase #7	$151.51	3.463%	$156.7568	$156.76	$156.75	$156.80
7 purchase totals =	$929.30		$1,004.3340	$1,004.33	$1,004.35	$1,004.20