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	$75.67	12.527%	$85.1492	$85.15	$85.15	$85.10
Purchase #2	$155.25	6.219%	$164.905	$164.91	$164.90	$164.90
Purchase #3	$49.52	9.309%	$54.1298	$54.13	$54.15	$54.10
Purchase #4	$148.83	12.215%	$167.0096	$167.01	$167.00	$167.00
Purchase #5	$86.89	13.767%	$98.8521	$98.85	$98.85	$98.90
Purchase #6	$140.45	11.766%	$156.9753	$156.98	$157.00	$157.00
Purchase #7	$136.44	7.112%	$146.1436	$146.14	$146.15	$146.10
7 purchase totals =	$793.05		$873.1646	$873.17	$873.20	$873.10