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	$74.61	8.799%	$81.1749	$81.17	$81.15	$81.20
Purchase #2	$100.32	11.483%	$111.8397	$111.84	$111.85	$111.80
Purchase #3	$142.63	3.116%	$147.0744	$147.07	$147.05	$147.10
Purchase #4	$6.53	9.197%	$7.1306	$7.13	$7.15	$7.10
Purchase #5	$183.53	4.637%	$192.0403	$192.04	$192.05	$192.00
Purchase #6	$90.50	4.515%	$94.5861	$94.59	$94.60	$94.60
Purchase #7	$40.48	6.421%	$43.0792	$43.08	$43.10	$43.10
7 purchase totals =	$638.60		$676.9252	$676.92	$676.95	$676.90