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	$107.52	5.641%	$113.5852	$113.59	$113.60	$113.60
Purchase #2	$117.38	12.306%	$131.8248	$131.82	$131.80	$131.80
Purchase #3	$36.96	5.390%	$38.9521	$38.95	$38.95	$39.00
Purchase #4	$82.55	3.131%	$85.1346	$85.13	$85.15	$85.10
Purchase #5	$23.90	7.515%	$25.6961	$25.70	$25.70	$25.70
Purchase #6	$101.53	11.214%	$112.9156	$112.92	$112.90	$112.90
Purchase #7	$149.63	4.414%	$156.2347	$156.23	$156.25	$156.20
7 purchase totals =	$619.47		$664.3431	$664.34	$664.35	$664.30