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	$9.29	4.759%	$9.7321	$9.73	$9.75	$9.70
Purchase #2	$100.85	4.828%	$105.719	$105.72	$105.70	$105.70
Purchase #3	$36.26	5.702%	$38.3275	$38.33	$38.35	$38.30
Purchase #4	$158.25	4.361%	$165.1513	$165.15	$165.15	$165.20
Purchase #5	$60.55	3.852%	$62.8824	$62.88	$62.90	$62.90
Purchase #6	$20.84	4.567%	$21.7918	$21.79	$21.80	$21.80
Purchase #7	$116.75	12.493%	$131.3356	$131.34	$131.35	$131.30
7 purchase totals =	$502.79		$534.9397	$534.94	$535.00	$534.90