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	$237.55	4.347%	$247.8763	$247.88	$247.90	$247.90
Purchase #2	$49.79	8.626%	$54.0849	$54.08	$54.10	$54.10
Purchase #3	$171.57	9.312%	$187.5466	$187.55	$187.55	$187.50
Purchase #4	$5.76	10.141%	$6.3441	$6.34	$6.35	$6.30
Purchase #5	$235.76	12.369%	$264.9212	$264.92	$264.90	$264.90
Purchase #6	$51.37	5.671%	$54.2832	$54.28	$54.30	$54.30
Purchase #7	$75.42	12.719%	$85.0127	$85.01	$85.00	$85.00
7 purchase totals =	$827.22		$900.0690	$900.06	$900.10	$900.00