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	$12.90	11.417%	$14.3728	$14.37	$14.35	$14.40
Purchase #2	$213.38	4.722%	$223.4558	$223.46	$223.45	$223.50
Purchase #3	$189.83	3.285%	$196.0659	$196.07	$196.05	$196.10
Purchase #4	$49.27	4.795%	$51.6325	$51.63	$51.65	$51.60
Purchase #5	$147.78	6.133%	$156.8433	$156.84	$156.85	$156.80
Purchase #6	$7.90	3.450%	$8.1726	$8.17	$8.15	$8.20
Purchase #7	$20.30	3.234%	$20.9565	$20.96	$20.95	$21.00
7 purchase totals =	$641.36		$671.4994	$671.50	$671.45	$671.60