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	$160.47	5.204%	$168.8209	$168.82	$168.80	$168.80
Purchase #2	$193.87	12.840%	$218.7629	$218.76	$218.75	$218.80
Purchase #3	$120.29	9.653%	$131.9016	$131.90	$131.90	$131.90
Purchase #4	$178.34	10.404%	$196.8945	$196.89	$196.90	$196.90
Purchase #5	$15.38	10.263%	$16.9584	$16.96	$16.95	$17.00
Purchase #6	$173.76	10.600%	$192.1786	$192.18	$192.20	$192.20
Purchase #7	$143.41	6.188%	$152.2842	$152.28	$152.30	$152.30
7 purchase totals =	$985.52		$1,077.8011	$1,077.79	$1,077.80	$1,077.90