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	$29.53	10.310%	$32.5745	$32.57	$32.55	$32.60
Purchase #2	$25.56	6.238%	$27.1544	$27.15	$27.15	$27.20
Purchase #3	$141.54	11.173%	$157.3543	$157.35	$157.35	$157.40
Purchase #4	$88.96	7.245%	$95.4052	$95.41	$95.40	$95.40
Purchase #5	$119.87	3.803%	$124.4287	$124.43	$124.45	$124.40
Purchase #6	$28.69	13.856%	$32.6653	$32.67	$32.65	$32.70
Purchase #7	$110.68	11.837%	$123.7812	$123.78	$123.80	$123.80
7 purchase totals =	$544.83		$593.3636	$593.36	$593.35	$593.50