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	$94.69	6.710%	$101.0437	$101.04	$101.05	$101.00
Purchase #2	$65.88	8.402%	$71.4152	$71.42	$71.40	$71.40
Purchase #3	$86.85	5.463%	$91.5946	$91.59	$91.60	$91.60
Purchase #4	$182.26	10.214%	$200.876	$200.88	$200.90	$200.90
Purchase #5	$96.64	10.193%	$106.4905	$106.49	$106.50	$106.50
Purchase #6	$5.58	13.773%	$6.3485	$6.35	$6.35	$6.30
Purchase #7	$81.96	7.789%	$88.3439	$88.34	$88.35	$88.30
7 purchase totals =	$613.86		$666.1124	$666.11	$666.15	$666.00