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	$226.66	8.188%	$245.2189	$245.22	$245.20	$245.20
Purchase #2	$146.56	6.709%	$156.3927	$156.39	$156.40	$156.40
Purchase #3	$51.28	10.800%	$56.8182	$56.82	$56.80	$56.80
Purchase #4	$235.69	5.757%	$249.2587	$249.26	$249.25	$249.30
Purchase #5	$51.43	5.752%	$54.3883	$54.39	$54.40	$54.40
Purchase #6	$36.45	8.501%	$39.5486	$39.55	$39.55	$39.50
Purchase #7	$91.57	12.810%	$103.3001	$103.30	$103.30	$103.30
7 purchase totals =	$839.64		$904.9255	$904.93	$904.90	$904.90