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	$99.54	13.331%	$112.8097	$112.81	$112.80	$112.80
Purchase #2	$53.93	9.401%	$59	$59.00	$59.00	$59.00
Purchase #3	$79.83	4.567%	$83.4758	$83.48	$83.50	$83.50
Purchase #4	$67.42	3.677%	$69.899	$69.90	$69.90	$69.90
Purchase #5	$103.74	5.218%	$109.1532	$109.15	$109.15	$109.20
Purchase #6	$122.58	12.156%	$137.4808	$137.48	$137.50	$137.50
Purchase #7	$39.55	8.720%	$42.9988	$43.00	$43.00	$43.00
7 purchase totals =	$566.59		$614.8173	$614.82	$614.85	$614.90