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	$82.83	8.538%	$89.902	$89.90	$89.90	$89.90
Purchase #2	$20.37	3.187%	$21.0192	$21.02	$21.00	$21.00
Purchase #3	$227.68	7.283%	$244.2619	$244.26	$244.25	$244.30
Purchase #4	$93.99	7.185%	$100.7432	$100.74	$100.75	$100.70
Purchase #5	$128.32	6.405%	$136.5389	$136.54	$136.55	$136.50
Purchase #6	$208.33	4.484%	$217.6715	$217.67	$217.65	$217.70
Purchase #7	$188.96	11.402%	$210.5052	$210.51	$210.50	$210.50
7 purchase totals =	$950.48		$1,020.6419	$1,020.64	$1,020.60	$1,020.60