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	$194.51	13.497%	$220.763	$220.76	$220.75	$220.80
Purchase #2	$210.49	10.756%	$233.1303	$233.13	$233.15	$233.10
Purchase #3	$72.29	13.628%	$82.1417	$82.14	$82.15	$82.10
Purchase #4	$62.70	13.414%	$71.1106	$71.11	$71.10	$71.10
Purchase #5	$81.75	6.156%	$86.7825	$86.78	$86.80	$86.80
Purchase #6	$238.92	8.755%	$259.8374	$259.84	$259.85	$259.80
Purchase #7	$156.58	3.520%	$162.0916	$162.09	$162.10	$162.10
7 purchase totals =	$1,017.24		$1,115.8571	$1,115.85	$1,115.90	$1,115.80