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	$234.94	9.169%	$256.4816	$256.48	$256.50	$256.50
Purchase #2	$125.34	11.151%	$139.3167	$139.32	$139.30	$139.30
Purchase #3	$121.36	6.804%	$129.6173	$129.62	$129.60	$129.60
Purchase #4	$244.68	3.517%	$253.2854	$253.29	$253.30	$253.30
Purchase #5	$203.75	9.871%	$223.8622	$223.86	$223.85	$223.90
Purchase #6	$141.27	10.543%	$156.1641	$156.16	$156.15	$156.20
Purchase #7	$28.95	10.275%	$31.9246	$31.92	$31.90	$31.90
7 purchase totals =	$1,100.29		$1,190.6519	$1,190.65	$1,190.60	$1,190.70