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	$233.85	11.382%	$260.4668	$260.47	$260.45	$260.50
Purchase #2	$130.63	7.189%	$140.021	$140.02	$140.00	$140.00
Purchase #3	$71.94	11.198%	$79.9958	$80.00	$80.00	$80.00
Purchase #4	$52.31	12.807%	$59.0093	$59.01	$59.00	$59.00
Purchase #5	$211.34	12.268%	$237.2672	$237.27	$237.25	$237.30
Purchase #6	$82.60	10.345%	$91.145	$91.15	$91.15	$91.10
Purchase #7	$78.79	8.649%	$85.6045	$85.60	$85.60	$85.60
7 purchase totals =	$861.46		$953.5096	$953.52	$953.45	$953.50