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	$35.75	13.543%	$40.5916	$40.59	$40.60	$40.60
Purchase #2	$119.64	11.550%	$133.4584	$133.46	$133.45	$133.50
Purchase #3	$226.64	6.604%	$241.6073	$241.61	$241.60	$241.60
Purchase #4	$159.45	6.215%	$169.3598	$169.36	$169.35	$169.40
Purchase #5	$191.27	4.742%	$200.34	$200.34	$200.35	$200.30
Purchase #6	$22.74	13.857%	$25.8911	$25.89	$25.90	$25.90
Purchase #7	$115.72	13.251%	$131.0541	$131.05	$131.05	$131.10
7 purchase totals =	$871.21		$942.3023	$942.30	$942.30	$942.40