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	$203.83	8.601%	$221.3614	$221.36	$221.35	$221.40
Purchase #2	$160.84	6.620%	$171.4876	$171.49	$171.50	$171.50
Purchase #3	$199.83	11.518%	$222.8464	$222.85	$222.85	$222.80
Purchase #4	$122.59	4.463%	$128.0612	$128.06	$128.05	$128.10
Purchase #5	$104.90	4.400%	$109.5156	$109.52	$109.50	$109.50
Purchase #6	$5.36	9.377%	$5.8626	$5.86	$5.85	$5.90
Purchase #7	$233.86	13.578%	$265.6135	$265.61	$265.60	$265.60
7 purchase totals =	$1,031.21		$1,124.7483	$1,124.75	$1,124.70	$1,124.80