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	$103.98	9.842%	$114.2137	$114.21	$114.20	$114.20
Purchase #2	$75.64	12.745%	$85.2803	$85.28	$85.30	$85.30
Purchase #3	$122.44	12.468%	$137.7058	$137.71	$137.70	$137.70
Purchase #4	$172.80	11.190%	$192.1363	$192.14	$192.15	$192.10
Purchase #5	$180.89	8.587%	$196.423	$196.42	$196.40	$196.40
Purchase #6	$42.30	3.759%	$43.8901	$43.89	$43.90	$43.90
Purchase #7	$58.37	11.121%	$64.8613	$64.86	$64.85	$64.90
7 purchase totals =	$756.42		$834.5105	$834.51	$834.50	$834.50