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	$77.37	6.145%	$82.1244	$82.12	$82.10	$82.10
Purchase #2	$162.75	3.198%	$167.9547	$167.95	$167.95	$168.00
Purchase #3	$103.45	6.671%	$110.3511	$110.35	$110.35	$110.40
Purchase #4	$226.66	5.373%	$238.8384	$238.84	$238.85	$238.80
Purchase #5	$39.63	13.551%	$45.0003	$45.00	$45.00	$45.00
Purchase #6	$176.33	8.638%	$191.5614	$191.56	$191.55	$191.60
Purchase #7	$132.67	13.727%	$150.8816	$150.88	$150.90	$150.90
7 purchase totals =	$918.86		$986.7119	$986.70	$986.70	$986.80