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	$73.86	10.806%	$81.8413	$81.84	$81.85	$81.80
Purchase #2	$116.54	4.189%	$121.4219	$121.42	$121.40	$121.40
Purchase #3	$95.94	7.244%	$102.8899	$102.89	$102.90	$102.90
Purchase #4	$32.98	7.779%	$35.5455	$35.55	$35.55	$35.50
Purchase #5	$93.77	6.529%	$99.8922	$99.89	$99.90	$99.90
Purchase #6	$73.45	13.544%	$83.3981	$83.40	$83.40	$83.40
Purchase #7	$67.47	4.115%	$70.2464	$70.25	$70.25	$70.20
7 purchase totals =	$554.01		$595.2353	$595.24	$595.25	$595.10