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	$109.77	4.118%	$114.2903	$114.29	$114.30	$114.30
Purchase #2	$83.60	10.824%	$92.6489	$92.65	$92.65	$92.60
Purchase #3	$76.77	11.318%	$85.4588	$85.46	$85.45	$85.50
Purchase #4	$21.29	11.489%	$23.736	$23.74	$23.75	$23.70
Purchase #5	$130.76	6.219%	$138.892	$138.89	$138.90	$138.90
Purchase #6	$108.71	13.659%	$123.5587	$123.56	$123.55	$123.60
Purchase #7	$54.66	12.360%	$61.416	$61.42	$61.40	$61.40
7 purchase totals =	$585.56		$640.0007	$640.01	$640.00	$640.00