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	$31.47	4.623%	$32.9249	$32.92	$32.90	$32.90
Purchase #2	$227.57	11.654%	$254.091	$254.09	$254.10	$254.10
Purchase #3	$55.72	11.240%	$61.9829	$61.98	$62.00	$62.00
Purchase #4	$102.77	7.459%	$110.4356	$110.44	$110.45	$110.40
Purchase #5	$122.77	11.453%	$136.8308	$136.83	$136.85	$136.80
Purchase #6	$38.69	4.257%	$40.337	$40.34	$40.35	$40.30
Purchase #7	$8.86	7.392%	$9.5149	$9.51	$9.50	$9.50
7 purchase totals =	$587.85		$646.1171	$646.11	$646.15	$646.00