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	$84.34	3.744%	$87.4977	$87.50	$87.50	$87.50
Purchase #2	$113.57	8.426%	$123.1394	$123.14	$123.15	$123.10
Purchase #3	$58.99	13.801%	$67.1312	$67.13	$67.15	$67.10
Purchase #4	$248.82	3.122%	$256.5882	$256.59	$256.60	$256.60
Purchase #5	$35.61	5.480%	$37.5614	$37.56	$37.55	$37.60
Purchase #6	$196.46	6.731%	$209.6837	$209.68	$209.70	$209.70
Purchase #7	$67.97	13.846%	$77.3811	$77.38	$77.40	$77.40
7 purchase totals =	$805.76		$858.9827	$858.98	$859.05	$859.00