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	$134.53	6.673%	$143.5072	$143.51	$143.50	$143.50
Purchase #2	$230.70	3.577%	$238.9521	$238.95	$238.95	$239.00
Purchase #3	$135.51	3.811%	$140.6743	$140.67	$140.65	$140.70
Purchase #4	$143.71	6.215%	$152.6416	$152.64	$152.65	$152.60
Purchase #5	$39.85	3.800%	$41.3643	$41.36	$41.35	$41.40
Purchase #6	$203.38	10.216%	$224.1573	$224.16	$224.15	$224.20
Purchase #7	$83.32	8.635%	$90.5147	$90.51	$90.50	$90.50
7 purchase totals =	$971.00		$1,031.8115	$1,031.80	$1,031.75	$1,031.90