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	$79.46	4.315%	$82.8887	$82.89	$82.90	$82.90
Purchase #2	$183.79	5.637%	$194.1502	$194.15	$194.15	$194.20
Purchase #3	$202.41	7.448%	$217.4855	$217.49	$217.50	$217.50
Purchase #4	$37.34	12.704%	$42.0837	$42.08	$42.10	$42.10
Purchase #5	$188.71	13.655%	$214.4784	$214.48	$214.50	$214.50
Purchase #6	$42.44	8.687%	$46.1268	$46.13	$46.15	$46.10
Purchase #7	$59.38	13.252%	$67.249	$67.25	$67.25	$67.20
7 purchase totals =	$793.53		$864.4623	$864.47	$864.55	$864.50