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	$222.53	9.186%	$242.9716	$242.97	$242.95	$243.00
Purchase #2	$90.54	11.211%	$100.6904	$100.69	$100.70	$100.70
Purchase #3	$48.86	7.123%	$52.3403	$52.34	$52.35	$52.30
Purchase #4	$237.34	11.767%	$265.2678	$265.27	$265.25	$265.30
Purchase #5	$90.41	6.605%	$96.3816	$96.38	$96.40	$96.40
Purchase #6	$57.41	13.376%	$65.0892	$65.09	$65.10	$65.10
Purchase #7	$244.36	9.770%	$268.234	$268.23	$268.25	$268.20
7 purchase totals =	$991.45		$1,090.9749	$1,090.97	$1,091.00	$1,091.00