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	$54.83	12.334%	$61.5927	$61.59	$61.60	$61.60
Purchase #2	$216.98	10.661%	$240.1122	$240.11	$240.10	$240.10
Purchase #3	$89.32	13.189%	$101.1004	$101.10	$101.10	$101.10
Purchase #4	$209.25	3.872%	$217.3522	$217.35	$217.35	$217.40
Purchase #5	$147.96	11.415%	$164.8496	$164.85	$164.85	$164.80
Purchase #6	$74.25	8.593%	$80.6303	$80.63	$80.65	$80.60
Purchase #7	$71.30	10.162%	$78.5455	$78.55	$78.55	$78.50
7 purchase totals =	$863.89		$944.1829	$944.18	$944.20	$944.10