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	$249.64	3.801%	$259.1288	$259.13	$259.15	$259.10
Purchase #2	$208.55	5.607%	$220.2434	$220.24	$220.25	$220.20
Purchase #3	$77.31	13.799%	$87.978	$87.98	$88.00	$88.00
Purchase #4	$28.59	11.407%	$31.8513	$31.85	$31.85	$31.90
Purchase #5	$128.33	7.804%	$138.3449	$138.34	$138.35	$138.30
Purchase #6	$215.95	3.666%	$223.8667	$223.87	$223.85	$223.90
Purchase #7	$167.81	7.542%	$180.4662	$180.47	$180.45	$180.50
7 purchase totals =	$1,076.18		$1,141.8793	$1,141.88	$1,141.90	$1,141.90