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	$189.72	5.729%	$200.5891	$200.59	$200.60	$200.60
Purchase #2	$13.62	12.467%	$15.318	$15.32	$15.30	$15.30
Purchase #3	$12.53	7.321%	$13.4473	$13.45	$13.45	$13.40
Purchase #4	$218.79	9.646%	$239.8945	$239.89	$239.90	$239.90
Purchase #5	$123.41	9.352%	$134.9513	$134.95	$134.95	$135.00
Purchase #6	$212.95	13.767%	$242.2668	$242.27	$242.25	$242.30
Purchase #7	$82.77	8.545%	$89.8427	$89.84	$89.85	$89.80
7 purchase totals =	$853.79		$936.3097	$936.31	$936.30	$936.30