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	$20.79	3.184%	$21.452	$21.45	$21.45	$21.50
Purchase #2	$224.45	7.402%	$241.0638	$241.06	$241.05	$241.10
Purchase #3	$92.83	7.155%	$99.472	$99.47	$99.45	$99.50
Purchase #4	$84.93	13.265%	$96.196	$96.20	$96.20	$96.20
Purchase #5	$154.42	7.112%	$165.4024	$165.40	$165.40	$165.40
Purchase #6	$57.53	11.150%	$63.9446	$63.94	$63.95	$63.90
Purchase #7	$156.28	5.163%	$164.3487	$164.35	$164.35	$164.30
7 purchase totals =	$791.23		$851.8795	$851.87	$851.85	$851.90