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	$67.88	6.642%	$72.3886	$72.39	$72.40	$72.40
Purchase #2	$27.83	5.363%	$29.3225	$29.32	$29.30	$29.30
Purchase #3	$236.73	3.595%	$245.2404	$245.24	$245.25	$245.20
Purchase #4	$104.57	13.743%	$118.9411	$118.94	$118.95	$118.90
Purchase #5	$204.95	7.305%	$219.9216	$219.92	$219.90	$219.90
Purchase #6	$57.85	5.359%	$60.9502	$60.95	$60.95	$61.00
Purchase #7	$179.66	6.185%	$190.772	$190.77	$190.75	$190.80
7 purchase totals =	$879.47		$937.5364	$937.53	$937.50	$937.50