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	$240.78	13.547%	$273.3985	$273.40	$273.40	$273.40
Purchase #2	$211.61	3.664%	$219.3634	$219.36	$219.35	$219.40
Purchase #3	$249.29	6.836%	$266.3315	$266.33	$266.35	$266.30
Purchase #4	$157.63	13.360%	$178.6894	$178.69	$178.70	$178.70
Purchase #5	$38.82	7.855%	$41.8693	$41.87	$41.85	$41.90
Purchase #6	$72.53	13.236%	$82.1301	$82.13	$82.15	$82.10
Purchase #7	$204.82	8.440%	$222.1068	$222.11	$222.10	$222.10
7 purchase totals =	$1,175.48		$1,283.8890	$1,283.89	$1,283.90	$1,283.90