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	$92.96	10.113%	$102.361	$102.36	$102.35	$102.40
Purchase #2	$247.25	8.206%	$267.5393	$267.54	$267.55	$267.50
Purchase #3	$45.73	10.233%	$50.4096	$50.41	$50.40	$50.40
Purchase #4	$162.58	9.802%	$178.5161	$178.52	$178.50	$178.50
Purchase #5	$35.51	9.703%	$38.9555	$38.96	$38.95	$39.00
Purchase #6	$58.73	7.651%	$63.2234	$63.22	$63.20	$63.20
Purchase #7	$99.33	12.321%	$111.5684	$111.57	$111.55	$111.60
7 purchase totals =	$742.09		$812.5733	$812.58	$812.50	$812.60