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	$30.33	10.812%	$33.6093	$33.61	$33.60	$33.60
Purchase #2	$124.85	13.370%	$141.5424	$141.54	$141.55	$141.50
Purchase #3	$197.54	12.632%	$222.4933	$222.49	$222.50	$222.50
Purchase #4	$17.31	10.663%	$19.1558	$19.16	$19.15	$19.20
Purchase #5	$227.59	6.220%	$241.7461	$241.75	$241.75	$241.70
Purchase #6	$97.28	9.431%	$106.4545	$106.45	$106.45	$106.50
Purchase #7	$165.94	10.828%	$183.908	$183.91	$183.90	$183.90
7 purchase totals =	$860.84		$948.9094	$948.91	$948.90	$948.90