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	$227.79	12.324%	$255.8628	$255.86	$255.85	$255.90
Purchase #2	$41.62	7.790%	$44.8622	$44.86	$44.85	$44.90
Purchase #3	$172.66	3.822%	$179.2591	$179.26	$179.25	$179.30
Purchase #4	$232.83	5.622%	$245.9197	$245.92	$245.90	$245.90
Purchase #5	$76.70	5.700%	$81.0719	$81.07	$81.05	$81.10
Purchase #6	$116.73	9.453%	$127.7645	$127.76	$127.75	$127.80
Purchase #7	$56.76	9.499%	$62.1516	$62.15	$62.15	$62.20
7 purchase totals =	$925.09		$996.8918	$996.88	$996.80	$997.10