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	$46.84	7.829%	$50.5071	$50.51	$50.50	$50.50
Purchase #2	$23.53	4.111%	$24.4973	$24.50	$24.50	$24.50
Purchase #3	$114.83	3.831%	$119.2291	$119.23	$119.25	$119.20
Purchase #4	$87.50	12.793%	$98.6939	$98.69	$98.70	$98.70
Purchase #5	$75.96	8.605%	$82.4964	$82.50	$82.50	$82.50
Purchase #6	$116.75	5.666%	$123.3651	$123.37	$123.35	$123.40
Purchase #7	$122.25	10.843%	$135.5056	$135.51	$135.50	$135.50
7 purchase totals =	$587.66		$634.2945	$634.31	$634.30	$634.30