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	$120.78	11.761%	$134.9849	$134.98	$135.00	$135.00
Purchase #2	$116.70	9.580%	$127.8799	$127.88	$127.90	$127.90
Purchase #3	$135.74	8.701%	$147.5507	$147.55	$147.55	$147.60
Purchase #4	$41.55	6.414%	$44.215	$44.22	$44.20	$44.20
Purchase #5	$59.60	8.127%	$64.4437	$64.44	$64.45	$64.40
Purchase #6	$52.91	12.820%	$59.6931	$59.69	$59.70	$59.70
Purchase #7	$28.95	9.273%	$31.6345	$31.63	$31.65	$31.60
7 purchase totals =	$556.23		$610.4018	$610.39	$610.45	$610.40