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	$93.44	8.731%	$101.5982	$101.60	$101.60	$101.60
Purchase #2	$144.81	5.850%	$153.2814	$153.28	$153.30	$153.30
Purchase #3	$154.67	9.184%	$168.8749	$168.87	$168.85	$168.90
Purchase #4	$53.90	9.812%	$59.1887	$59.19	$59.20	$59.20
Purchase #5	$235.51	6.218%	$250.154	$250.15	$250.15	$250.20
Purchase #6	$39.83	5.293%	$41.9382	$41.94	$41.95	$41.90
Purchase #7	$194.67	4.765%	$203.946	$203.95	$203.95	$203.90
7 purchase totals =	$916.83		$978.9814	$978.98	$979.00	$979.00