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	$47.59	6.798%	$50.8252	$50.83	$50.85	$50.80
Purchase #2	$185.72	11.263%	$206.6376	$206.64	$206.65	$206.60
Purchase #3	$56.48	7.394%	$60.6561	$60.66	$60.65	$60.70
Purchase #4	$50.88	8.620%	$55.2659	$55.27	$55.25	$55.30
Purchase #5	$41.53	3.350%	$42.9213	$42.92	$42.90	$42.90
Purchase #6	$237.50	12.777%	$267.8454	$267.85	$267.85	$267.80
Purchase #7	$135.72	4.252%	$141.4908	$141.49	$141.50	$141.50
7 purchase totals =	$755.42		$825.6423	$825.66	$825.65	$825.60