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	$29.73	13.431%	$33.723	$33.72	$33.70	$33.70
Purchase #2	$133.33	4.385%	$139.1765	$139.18	$139.20	$139.20
Purchase #3	$113.66	12.687%	$128.08	$128.08	$128.10	$128.10
Purchase #4	$97.39	9.743%	$106.8787	$106.88	$106.90	$106.90
Purchase #5	$175.28	9.117%	$191.2603	$191.26	$191.25	$191.30
Purchase #6	$229.53	11.319%	$255.5105	$255.51	$255.50	$255.50
Purchase #7	$39.81	5.154%	$41.8618	$41.86	$41.85	$41.90
7 purchase totals =	$818.73		$896.4908	$896.49	$896.50	$896.60