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	$18.81	4.853%	$19.7228	$19.72	$19.70	$19.70
Purchase #2	$220.90	12.686%	$248.9234	$248.92	$248.90	$248.90
Purchase #3	$186.78	6.797%	$199.4754	$199.48	$199.50	$199.50
Purchase #4	$113.36	4.513%	$118.4759	$118.48	$118.50	$118.50
Purchase #5	$87.92	13.574%	$99.8543	$99.85	$99.85	$99.90
Purchase #6	$62.57	8.126%	$67.6544	$67.65	$67.65	$67.70
Purchase #7	$34.33	10.462%	$37.9216	$37.92	$37.90	$37.90
7 purchase totals =	$724.67		$792.0278	$792.02	$792.00	$792.10