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	$87.49	3.302%	$90.3789	$90.38	$90.40	$90.40
Purchase #2	$91.62	8.837%	$99.7165	$99.72	$99.70	$99.70
Purchase #3	$53.82	5.833%	$56.9593	$56.96	$56.95	$57.00
Purchase #4	$232.71	8.623%	$252.7766	$252.78	$252.80	$252.80
Purchase #5	$50.70	9.464%	$55.4982	$55.50	$55.50	$55.50
Purchase #6	$32.49	9.426%	$35.5525	$35.55	$35.55	$35.60
Purchase #7	$167.45	7.109%	$179.354	$179.35	$179.35	$179.40
7 purchase totals =	$716.28		$770.2360	$770.24	$770.25	$770.40