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	$212.34	8.288%	$229.9387	$229.94	$229.95	$229.90
Purchase #2	$168.71	11.382%	$187.9126	$187.91	$187.90	$187.90
Purchase #3	$77.27	8.548%	$83.875	$83.88	$83.90	$83.90
Purchase #4	$146.72	5.599%	$154.9349	$154.93	$154.95	$154.90
Purchase #5	$100.60	4.711%	$105.3393	$105.34	$105.35	$105.30
Purchase #6	$245.44	10.178%	$270.4209	$270.42	$270.40	$270.40
Purchase #7	$91.94	9.654%	$100.8159	$100.82	$100.80	$100.80
7 purchase totals =	$1,043.02		$1,133.2373	$1,133.24	$1,133.25	$1,133.10