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	$238.39	13.339%	$270.1888	$270.19	$270.20	$270.20
Purchase #2	$84.73	6.628%	$90.3459	$90.35	$90.35	$90.30
Purchase #3	$49.91	8.448%	$54.1264	$54.13	$54.15	$54.10
Purchase #4	$26.44	8.684%	$28.736	$28.74	$28.75	$28.70
Purchase #5	$183.87	6.662%	$196.1194	$196.12	$196.10	$196.10
Purchase #6	$86.28	8.839%	$93.9063	$93.91	$93.90	$93.90
Purchase #7	$35.32	4.786%	$37.0104	$37.01	$37.00	$37.00
7 purchase totals =	$704.94		$770.4332	$770.45	$770.45	$770.30