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	$128.82	5.657%	$136.1073	$136.11	$136.10	$136.10
Purchase #2	$158.95	12.408%	$178.6725	$178.67	$178.65	$178.70
Purchase #3	$211.92	6.282%	$225.2328	$225.23	$225.25	$225.20
Purchase #4	$63.47	12.365%	$71.3181	$71.32	$71.30	$71.30
Purchase #5	$173.76	5.658%	$183.5913	$183.59	$183.60	$183.60
Purchase #6	$80.86	6.231%	$85.8984	$85.90	$85.90	$85.90
Purchase #7	$215.30	12.840%	$242.9445	$242.94	$242.95	$242.90
7 purchase totals =	$1,033.08		$1,123.7649	$1,123.76	$1,123.75	$1,123.70