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	$198.62	11.709%	$221.8764	$221.88	$221.90	$221.90
Purchase #2	$19.96	8.252%	$21.6071	$21.61	$21.60	$21.60
Purchase #3	$137.54	3.792%	$142.7555	$142.76	$142.75	$142.80
Purchase #4	$190.43	13.206%	$215.5782	$215.58	$215.60	$215.60
Purchase #5	$49.38	13.616%	$56.1036	$56.10	$56.10	$56.10
Purchase #6	$6.93	12.413%	$7.7902	$7.79	$7.80	$7.80
Purchase #7	$152.98	7.427%	$164.3418	$164.34	$164.35	$164.30
7 purchase totals =	$755.84		$830.0528	$830.06	$830.10	$830.10