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	$77.51	8.818%	$84.3448	$84.34	$84.35	$84.30
Purchase #2	$53.33	11.196%	$59.3008	$59.30	$59.30	$59.30
Purchase #3	$26.56	11.456%	$29.6027	$29.60	$29.60	$29.60
Purchase #4	$73.25	11.744%	$81.8525	$81.85	$81.85	$81.90
Purchase #5	$104.69	13.228%	$118.5384	$118.54	$118.55	$118.50
Purchase #6	$52.44	12.815%	$59.1602	$59.16	$59.15	$59.20
Purchase #7	$116.90	13.654%	$132.8615	$132.86	$132.85	$132.90
7 purchase totals =	$504.68		$565.6609	$565.65	$565.65	$565.70