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	$48.87	3.173%	$50.4206	$50.42	$50.40	$50.40
Purchase #2	$162.50	8.670%	$176.5888	$176.59	$176.60	$176.60
Purchase #3	$19.50	10.664%	$21.5795	$21.58	$21.60	$21.60
Purchase #4	$210.89	4.820%	$221.0549	$221.05	$221.05	$221.10
Purchase #5	$115.77	7.599%	$124.5674	$124.57	$124.55	$124.60
Purchase #6	$95.67	11.744%	$106.9055	$106.91	$106.90	$106.90
Purchase #7	$88.46	12.712%	$99.705	$99.71	$99.70	$99.70
7 purchase totals =	$741.66		$800.8217	$800.83	$800.80	$800.90