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	$142.55	11.764%	$159.3196	$159.32	$159.30	$159.30
Purchase #2	$145.40	12.789%	$163.9952	$164.00	$164.00	$164.00
Purchase #3	$67.35	7.656%	$72.5063	$72.51	$72.50	$72.50
Purchase #4	$150.79	9.760%	$165.5071	$165.51	$165.50	$165.50
Purchase #5	$242.91	8.173%	$262.763	$262.76	$262.75	$262.80
Purchase #6	$6.88	11.208%	$7.6511	$7.65	$7.65	$7.70
Purchase #7	$246.41	8.618%	$267.6456	$267.65	$267.65	$267.60
7 purchase totals =	$1,002.29		$1,099.3879	$1,099.40	$1,099.35	$1,099.40