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	$175.69	7.837%	$189.4588	$189.46	$189.45	$189.50
Purchase #2	$61.74	3.771%	$64.0682	$64.07	$64.05	$64.10
Purchase #3	$131.57	4.201%	$137.0973	$137.10	$137.10	$137.10
Purchase #4	$222.46	13.848%	$253.2663	$253.27	$253.25	$253.30
Purchase #5	$15.41	3.111%	$15.8894	$15.89	$15.90	$15.90
Purchase #6	$162.43	3.405%	$167.9607	$167.96	$167.95	$168.00
Purchase #7	$109.83	6.160%	$116.5955	$116.60	$116.60	$116.60
7 purchase totals =	$879.13		$944.3362	$944.35	$944.30	$944.50