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	$17.72	4.233%	$18.4701	$18.47	$18.45	$18.50
Purchase #2	$202.90	5.291%	$213.6354	$213.64	$213.65	$213.60
Purchase #3	$227.72	11.536%	$253.9898	$253.99	$254.00	$254.00
Purchase #4	$94.85	4.788%	$99.3914	$99.39	$99.40	$99.40
Purchase #5	$237.82	11.375%	$264.872	$264.87	$264.85	$264.90
Purchase #6	$12.42	11.620%	$13.8632	$13.86	$13.85	$13.90
Purchase #7	$201.58	13.373%	$228.5373	$228.54	$228.55	$228.50
7 purchase totals =	$995.01		$1,092.7592	$1,092.76	$1,092.75	$1,092.80