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	$5.60	5.336%	$5.8988	$5.90	$5.90	$5.90
Purchase #2	$116.64	6.176%	$123.8437	$123.84	$123.85	$123.80
Purchase #3	$205.71	6.293%	$218.6553	$218.66	$218.65	$218.70
Purchase #4	$199.34	11.738%	$222.7385	$222.74	$222.75	$222.70
Purchase #5	$243.70	9.574%	$267.0318	$267.03	$267.05	$267.00
Purchase #6	$40.76	3.556%	$42.2094	$42.21	$42.20	$42.20
Purchase #7	$167.56	10.747%	$185.5677	$185.57	$185.55	$185.60
7 purchase totals =	$979.31		$1,065.9452	$1,065.95	$1,065.95	$1,065.90