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	$150.87	3.658%	$156.3888	$156.39	$156.40	$156.40
Purchase #2	$121.88	3.482%	$126.1239	$126.12	$126.10	$126.10
Purchase #3	$245.83	7.582%	$264.4688	$264.47	$264.45	$264.50
Purchase #4	$71.60	12.700%	$80.6932	$80.69	$80.70	$80.70
Purchase #5	$95.76	10.320%	$105.6424	$105.64	$105.65	$105.60
Purchase #6	$59.34	7.202%	$63.6137	$63.61	$63.60	$63.60
Purchase #7	$74.50	4.330%	$77.7259	$77.73	$77.75	$77.70
7 purchase totals =	$819.78		$874.6567	$874.65	$874.65	$874.60