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	$134.36	13.802%	$152.9044	$152.90	$152.90	$152.90
Purchase #2	$38.94	7.349%	$41.8017	$41.80	$41.80	$41.80
Purchase #3	$230.51	3.393%	$238.3312	$238.33	$238.35	$238.30
Purchase #4	$88.78	8.157%	$96.0218	$96.02	$96.00	$96.00
Purchase #5	$112.77	11.240%	$125.4453	$125.45	$125.45	$125.40
Purchase #6	$188.54	5.619%	$199.1341	$199.13	$199.15	$199.10
Purchase #7	$46.25	9.240%	$50.5235	$50.52	$50.50	$50.50
7 purchase totals =	$840.15		$904.1620	$904.15	$904.15	$904.00