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	$40.87	3.316%	$42.2252	$42.23	$42.25	$42.20
Purchase #2	$45.86	5.315%	$48.2975	$48.30	$48.30	$48.30
Purchase #3	$29.62	5.333%	$31.1996	$31.20	$31.20	$31.20
Purchase #4	$148.88	9.166%	$162.5263	$162.53	$162.55	$162.50
Purchase #5	$79.68	3.530%	$82.4927	$82.49	$82.50	$82.50
Purchase #6	$65.52	8.519%	$71.1016	$71.10	$71.10	$71.10
Purchase #7	$71.84	12.453%	$80.7862	$80.79	$80.80	$80.80
7 purchase totals =	$482.27		$518.6291	$518.64	$518.70	$518.60