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	$50.66	9.156%	$55.2984	$55.30	$55.30	$55.30
Purchase #2	$44.27	7.768%	$47.7089	$47.71	$47.70	$47.70
Purchase #3	$215.80	13.720%	$245.4078	$245.41	$245.40	$245.40
Purchase #4	$86.33	11.275%	$96.0637	$96.06	$96.05	$96.10
Purchase #5	$12.54	10.316%	$13.8336	$13.83	$13.85	$13.80
Purchase #6	$75.48	11.205%	$83.9375	$83.94	$83.95	$83.90
Purchase #7	$111.54	10.582%	$123.3432	$123.34	$123.35	$123.30
7 purchase totals =	$596.62		$665.5931	$665.59	$665.60	$665.50