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	$226.86	10.423%	$250.5056	$250.51	$250.50	$250.50
Purchase #2	$198.50	10.372%	$219.0884	$219.09	$219.10	$219.10
Purchase #3	$60.74	8.802%	$66.0863	$66.09	$66.10	$66.10
Purchase #4	$48.52	6.168%	$51.5127	$51.51	$51.50	$51.50
Purchase #5	$69.95	7.660%	$75.3082	$75.31	$75.30	$75.30
Purchase #6	$78.28	10.312%	$86.3522	$86.35	$86.35	$86.40
Purchase #7	$115.35	10.551%	$127.5206	$127.52	$127.50	$127.50
7 purchase totals =	$798.20		$876.3740	$876.38	$876.35	$876.40