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	$34.37	7.261%	$36.8656	$36.87	$36.85	$36.90
Purchase #2	$231.60	5.185%	$243.6085	$243.61	$243.60	$243.60
Purchase #3	$65.79	9.392%	$71.969	$71.97	$71.95	$72.00
Purchase #4	$159.75	8.592%	$173.4757	$173.48	$173.50	$173.50
Purchase #5	$127.62	13.433%	$144.7632	$144.76	$144.75	$144.80
Purchase #6	$158.61	6.423%	$168.7975	$168.80	$168.80	$168.80
Purchase #7	$96.59	3.407%	$99.8808	$99.88	$99.90	$99.90
7 purchase totals =	$874.33		$939.3603	$939.37	$939.35	$939.50