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	$103.51	9.795%	$113.6488	$113.65	$113.65	$113.60
Purchase #2	$135.41	4.777%	$141.8785	$141.88	$141.90	$141.90
Purchase #3	$30.75	11.204%	$34.1952	$34.20	$34.20	$34.20
Purchase #4	$240.94	11.817%	$269.4119	$269.41	$269.40	$269.40
Purchase #5	$24.85	4.311%	$25.9213	$25.92	$25.90	$25.90
Purchase #6	$43.65	3.803%	$45.31	$45.31	$45.30	$45.30
Purchase #7	$172.86	10.141%	$190.3897	$190.39	$190.40	$190.40
7 purchase totals =	$751.97		$820.7554	$820.76	$820.75	$820.70