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	$101.85	11.442%	$113.5037	$113.50	$113.50	$113.50
Purchase #2	$75.93	3.245%	$78.3939	$78.39	$78.40	$78.40
Purchase #3	$22.97	12.635%	$25.8723	$25.87	$25.85	$25.90
Purchase #4	$250.33	11.821%	$279.9215	$279.92	$279.90	$279.90
Purchase #5	$172.34	7.811%	$185.8015	$185.80	$185.80	$185.80
Purchase #6	$100.99	11.286%	$112.3877	$112.39	$112.40	$112.40
Purchase #7	$215.25	9.631%	$235.9807	$235.98	$236.00	$236.00
7 purchase totals =	$939.66		$1,031.8613	$1,031.85	$1,031.85	$1,031.90