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	$9.85	6.752%	$10.5151	$10.52	$10.50	$10.50
Purchase #2	$55.59	11.215%	$61.8244	$61.82	$61.80	$61.80
Purchase #3	$120.71	3.787%	$125.2813	$125.28	$125.30	$125.30
Purchase #4	$198.36	8.808%	$215.8315	$215.83	$215.85	$215.80
Purchase #5	$243.61	8.709%	$264.826	$264.83	$264.85	$264.80
Purchase #6	$71.34	8.115%	$77.1292	$77.13	$77.15	$77.10
Purchase #7	$215.30	6.387%	$229.0512	$229.05	$229.05	$229.10
7 purchase totals =	$914.76		$984.4587	$984.46	$984.50	$984.40