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	$48.96	8.532%	$53.1373	$53.14	$53.15	$53.10
Purchase #2	$95.40	9.200%	$104.1768	$104.18	$104.20	$104.20
Purchase #3	$99.79	5.474%	$105.2525	$105.25	$105.25	$105.30
Purchase #4	$220.46	8.703%	$239.6466	$239.65	$239.65	$239.60
Purchase #5	$215.78	7.469%	$231.8966	$231.90	$231.90	$231.90
Purchase #6	$53.53	3.645%	$55.4812	$55.48	$55.50	$55.50
Purchase #7	$88.62	12.715%	$99.888	$99.89	$99.90	$99.90
7 purchase totals =	$822.54		$889.4790	$889.49	$889.55	$889.50