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	$166.88	11.409%	$185.9193	$185.92	$185.90	$185.90
Purchase #2	$178.34	5.279%	$187.7546	$187.75	$187.75	$187.80
Purchase #3	$86.57	6.526%	$92.2196	$92.22	$92.20	$92.20
Purchase #4	$25.77	13.805%	$29.3275	$29.33	$29.35	$29.30
Purchase #5	$216.80	11.575%	$241.8946	$241.89	$241.90	$241.90
Purchase #6	$6.95	6.679%	$7.4142	$7.41	$7.40	$7.40
Purchase #7	$241.90	4.699%	$253.2669	$253.27	$253.25	$253.30
7 purchase totals =	$923.21		$997.7967	$997.79	$997.75	$997.80