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	$83.73	8.826%	$91.12	$91.12	$91.10	$91.10
Purchase #2	$39.72	7.822%	$42.8269	$42.83	$42.85	$42.80
Purchase #3	$143.53	6.560%	$152.9456	$152.95	$152.95	$152.90
Purchase #4	$136.51	4.647%	$142.8536	$142.85	$142.85	$142.90
Purchase #5	$211.85	4.158%	$220.6587	$220.66	$220.65	$220.70
Purchase #6	$66.66	9.720%	$73.1394	$73.14	$73.15	$73.10
Purchase #7	$51.69	10.303%	$57.0156	$57.02	$57.00	$57.00
7 purchase totals =	$733.69		$780.5598	$780.57	$780.55	$780.50