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	$72.88	10.126%	$80.2598	$80.26	$80.25	$80.30
Purchase #2	$68.76	13.606%	$78.1155	$78.12	$78.10	$78.10
Purchase #3	$114.26	12.809%	$128.8956	$128.90	$128.90	$128.90
Purchase #4	$227.69	9.743%	$249.8738	$249.87	$249.85	$249.90
Purchase #5	$237.59	7.550%	$255.528	$255.53	$255.55	$255.50
Purchase #6	$93.83	12.569%	$105.6235	$105.62	$105.60	$105.60
Purchase #7	$75.31	13.850%	$85.7404	$85.74	$85.75	$85.70
7 purchase totals =	$890.32		$984.0366	$984.04	$984.00	$984.00