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	$108.84	11.223%	$121.0551	$121.06	$121.05	$121.10
Purchase #2	$43.85	3.332%	$45.3111	$45.31	$45.30	$45.30
Purchase #3	$183.72	3.830%	$190.7565	$190.76	$190.75	$190.80
Purchase #4	$220.82	8.685%	$239.9982	$240.00	$240.00	$240.00
Purchase #5	$55.34	11.709%	$61.8198	$61.82	$61.80	$61.80
Purchase #6	$102.40	6.731%	$109.2925	$109.29	$109.30	$109.30
Purchase #7	$85.81	13.288%	$97.2124	$97.21	$97.20	$97.20
7 purchase totals =	$800.78		$865.4456	$865.45	$865.40	$865.50