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	$228.91	12.340%	$257.1575	$257.16	$257.15	$257.20
Purchase #2	$111.98	9.472%	$122.5867	$122.59	$122.60	$122.60
Purchase #3	$91.81	13.115%	$103.8509	$103.85	$103.85	$103.90
Purchase #4	$55.36	7.813%	$59.6853	$59.69	$59.70	$59.70
Purchase #5	$120.71	9.130%	$131.7308	$131.73	$131.75	$131.70
Purchase #6	$82.50	13.780%	$93.8685	$93.87	$93.85	$93.90
Purchase #7	$142.62	6.725%	$152.2112	$152.21	$152.20	$152.20
7 purchase totals =	$833.89		$921.0909	$921.10	$921.10	$921.20