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	$8.79	13.839%	$10.0064	$10.01	$10.00	$10.00
Purchase #2	$75.63	4.310%	$78.8897	$78.89	$78.90	$78.90
Purchase #3	$182.98	11.255%	$203.5744	$203.57	$203.55	$203.60
Purchase #4	$250.85	4.109%	$261.1574	$261.16	$261.15	$261.20
Purchase #5	$105.68	4.387%	$110.3162	$110.32	$110.30	$110.30
Purchase #6	$37.73	6.485%	$40.1768	$40.18	$40.20	$40.20
Purchase #7	$199.59	5.467%	$210.5016	$210.50	$210.50	$210.50
7 purchase totals =	$861.25		$914.6225	$914.63	$914.60	$914.70