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	$144.25	11.157%	$160.344	$160.34	$160.35	$160.30
Purchase #2	$91.64	3.551%	$94.8941	$94.89	$94.90	$94.90
Purchase #3	$114.33	12.678%	$128.8248	$128.82	$128.80	$128.80
Purchase #4	$7.59	4.600%	$7.9391	$7.94	$7.95	$7.90
Purchase #5	$5.35	12.206%	$6.003	$6.00	$6.00	$6.00
Purchase #6	$100.93	10.732%	$111.7618	$111.76	$111.75	$111.80
Purchase #7	$120.91	9.624%	$132.5464	$132.55	$132.55	$132.50
7 purchase totals =	$585.00		$642.3132	$642.30	$642.30	$642.20