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	$42.98	7.515%	$46.2099	$46.21	$46.20	$46.20
Purchase #2	$58.78	3.607%	$60.9002	$60.90	$60.90	$60.90
Purchase #3	$23.50	7.702%	$25.31	$25.31	$25.30	$25.30
Purchase #4	$223.62	11.563%	$249.4772	$249.48	$249.50	$249.50
Purchase #5	$12.86	11.569%	$14.3478	$14.35	$14.35	$14.30
Purchase #6	$203.47	9.322%	$222.4375	$222.44	$222.45	$222.40
Purchase #7	$199.25	11.426%	$222.0163	$222.02	$222.00	$222.00
7 purchase totals =	$764.46		$840.6989	$840.71	$840.70	$840.60