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	$231.44	10.556%	$255.8708	$255.87	$255.85	$255.90
Purchase #2	$75.95	8.452%	$82.3693	$82.37	$82.35	$82.40
Purchase #3	$81.73	10.179%	$90.0493	$90.05	$90.05	$90.00
Purchase #4	$204.27	8.150%	$220.918	$220.92	$220.90	$220.90
Purchase #5	$223.95	9.855%	$246.0203	$246.02	$246.00	$246.00
Purchase #6	$59.72	8.815%	$64.9843	$64.98	$65.00	$65.00
Purchase #7	$81.88	10.672%	$90.6182	$90.62	$90.60	$90.60
7 purchase totals =	$958.94		$1,050.8302	$1,050.83	$1,050.75	$1,050.80