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	$60.83	7.107%	$65.1532	$65.15	$65.15	$65.20
Purchase #2	$237.76	3.141%	$245.228	$245.23	$245.25	$245.20
Purchase #3	$82.63	6.733%	$88.1935	$88.19	$88.20	$88.20
Purchase #4	$131.53	12.800%	$148.3658	$148.37	$148.35	$148.40
Purchase #5	$200.27	7.442%	$215.1741	$215.17	$215.15	$215.20
Purchase #6	$82.46	7.871%	$88.9504	$88.95	$88.95	$89.00
Purchase #7	$117.91	8.441%	$127.8628	$127.86	$127.85	$127.90
7 purchase totals =	$913.39		$978.9278	$978.92	$978.90	$979.10