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	$115.88	11.607%	$129.3302	$129.33	$129.35	$129.30
Purchase #2	$182.65	5.497%	$192.6903	$192.69	$192.70	$192.70
Purchase #3	$126.43	4.235%	$131.7843	$131.78	$131.80	$131.80
Purchase #4	$60.58	10.520%	$66.953	$66.95	$66.95	$67.00
Purchase #5	$156.95	7.387%	$168.5439	$168.54	$168.55	$168.50
Purchase #6	$35.54	7.668%	$38.2652	$38.27	$38.25	$38.30
Purchase #7	$49.82	13.374%	$56.4829	$56.48	$56.50	$56.50
7 purchase totals =	$727.85		$784.0498	$784.04	$784.10	$784.10