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	$120.85	9.442%	$132.2607	$132.26	$132.25	$132.30
Purchase #2	$108.71	13.847%	$123.7631	$123.76	$123.75	$123.80
Purchase #3	$199.82	10.558%	$220.917	$220.92	$220.90	$220.90
Purchase #4	$41.34	5.439%	$43.5885	$43.59	$43.60	$43.60
Purchase #5	$231.84	8.123%	$250.6724	$250.67	$250.65	$250.70
Purchase #6	$205.76	12.712%	$231.9162	$231.92	$231.90	$231.90
Purchase #7	$52.37	11.430%	$58.3559	$58.36	$58.35	$58.40
7 purchase totals =	$960.69		$1,061.4738	$1,061.48	$1,061.40	$1,061.60