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	$83.30	9.856%	$91.51	$91.51	$91.50	$91.50
Purchase #2	$155.77	7.454%	$167.3811	$167.38	$167.40	$167.40
Purchase #3	$40.67	6.472%	$43.3022	$43.30	$43.30	$43.30
Purchase #4	$142.98	10.443%	$157.9114	$157.91	$157.90	$157.90
Purchase #5	$92.89	6.599%	$99.0198	$99.02	$99.00	$99.00
Purchase #6	$160.93	9.628%	$176.4243	$176.42	$176.40	$176.40
Purchase #7	$93.38	3.801%	$96.9294	$96.93	$96.95	$96.90
7 purchase totals =	$769.92		$832.4782	$832.47	$832.45	$832.40