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	$79.60	12.187%	$89.3009	$89.30	$89.30	$89.30
Purchase #2	$56.52	4.792%	$59.2284	$59.23	$59.25	$59.20
Purchase #3	$172.89	12.306%	$194.1658	$194.17	$194.15	$194.20
Purchase #4	$119.60	13.685%	$135.9673	$135.97	$135.95	$136.00
Purchase #5	$125.91	8.200%	$136.2346	$136.23	$136.25	$136.20
Purchase #6	$45.44	8.281%	$49.2029	$49.20	$49.20	$49.20
Purchase #7	$173.80	13.182%	$196.7103	$196.71	$196.70	$196.70
7 purchase totals =	$773.76		$860.8102	$860.81	$860.80	$860.80