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	$56.69	4.393%	$59.1804	$59.18	$59.20	$59.20
Purchase #2	$31.49	7.142%	$33.739	$33.74	$33.75	$33.70
Purchase #3	$48.94	6.664%	$52.2014	$52.20	$52.20	$52.20
Purchase #4	$123.54	6.800%	$131.9407	$131.94	$131.95	$131.90
Purchase #5	$99.80	3.724%	$103.5166	$103.52	$103.50	$103.50
Purchase #6	$200.56	8.805%	$218.2193	$218.22	$218.20	$218.20
Purchase #7	$205.37	8.433%	$222.6889	$222.69	$222.70	$222.70
7 purchase totals =	$766.39		$821.4863	$821.49	$821.50	$821.40