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	$93.38	8.328%	$101.1567	$101.16	$101.15	$101.20
Purchase #2	$38.26	5.534%	$40.3773	$40.38	$40.40	$40.40
Purchase #3	$52.59	10.377%	$58.0473	$58.05	$58.05	$58.00
Purchase #4	$84.29	13.399%	$95.584	$95.58	$95.60	$95.60
Purchase #5	$242.89	9.376%	$265.6634	$265.66	$265.65	$265.70
Purchase #6	$74.51	12.553%	$83.8632	$83.86	$83.85	$83.90
Purchase #7	$100.28	8.859%	$109.1638	$109.16	$109.15	$109.20
7 purchase totals =	$686.20		$753.8557	$753.85	$753.85	$754.00