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	$96.49	9.129%	$105.2986	$105.30	$105.30	$105.30
Purchase #2	$123.35	5.296%	$129.8826	$129.88	$129.90	$129.90
Purchase #3	$191.28	6.815%	$204.3157	$204.32	$204.30	$204.30
Purchase #4	$124.45	12.225%	$139.664	$139.66	$139.65	$139.70
Purchase #5	$147.51	10.131%	$162.4542	$162.45	$162.45	$162.50
Purchase #6	$110.59	11.533%	$123.3443	$123.34	$123.35	$123.30
Purchase #7	$66.35	11.417%	$73.9252	$73.93	$73.95	$73.90
7 purchase totals =	$860.02		$938.8846	$938.88	$938.90	$938.90