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	$78.79	13.108%	$89.1178	$89.12	$89.10	$89.10
Purchase #2	$77.52	4.625%	$81.1053	$81.11	$81.10	$81.10
Purchase #3	$69.45	6.391%	$73.8885	$73.89	$73.90	$73.90
Purchase #4	$28.53	12.567%	$32.1154	$32.12	$32.10	$32.10
Purchase #5	$89.42	9.352%	$97.7826	$97.78	$97.80	$97.80
Purchase #6	$180.69	12.804%	$203.8255	$203.83	$203.85	$203.80
Purchase #7	$134.92	6.567%	$143.7802	$143.78	$143.80	$143.80
7 purchase totals =	$659.32		$721.6153	$721.63	$721.65	$721.60