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	$18.55	5.286%	$19.5306	$19.53	$19.55	$19.50
Purchase #2	$234.66	3.747%	$243.4527	$243.45	$243.45	$243.50
Purchase #3	$137.49	3.460%	$142.2472	$142.25	$142.25	$142.20
Purchase #4	$129.98	9.183%	$141.9161	$141.92	$141.90	$141.90
Purchase #5	$90.48	10.439%	$99.9252	$99.93	$99.95	$99.90
Purchase #6	$59.74	10.363%	$65.9309	$65.93	$65.95	$65.90
Purchase #7	$52.65	7.238%	$56.4608	$56.46	$56.45	$56.50
7 purchase totals =	$723.55		$769.4635	$769.47	$769.50	$769.40