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	$147.84	5.768%	$156.3674	$156.37	$156.35	$156.40
Purchase #2	$75.53	4.436%	$78.8805	$78.88	$78.90	$78.90
Purchase #3	$227.84	11.108%	$253.1485	$253.15	$253.15	$253.10
Purchase #4	$139.59	11.146%	$155.1487	$155.15	$155.15	$155.10
Purchase #5	$71.90	11.846%	$80.4173	$80.42	$80.40	$80.40
Purchase #6	$37.49	8.566%	$40.7014	$40.70	$40.70	$40.70
Purchase #7	$17.34	5.336%	$18.2653	$18.27	$18.25	$18.30
7 purchase totals =	$717.53		$782.9291	$782.94	$782.90	$782.90