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	$122.47	7.266%	$131.3687	$131.37	$131.35	$131.40
Purchase #2	$83.97	7.309%	$90.1074	$90.11	$90.10	$90.10
Purchase #3	$80.45	12.299%	$90.3445	$90.34	$90.35	$90.30
Purchase #4	$74.33	13.679%	$84.4976	$84.50	$84.50	$84.50
Purchase #5	$103.63	9.697%	$113.679	$113.68	$113.70	$113.70
Purchase #6	$243.76	6.534%	$259.6873	$259.69	$259.70	$259.70
Purchase #7	$135.92	10.783%	$150.5763	$150.58	$150.60	$150.60
7 purchase totals =	$844.53		$920.2608	$920.27	$920.30	$920.30