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	$41.46	3.165%	$42.7722	$42.77	$42.75	$42.80
Purchase #2	$187.96	10.332%	$207.38	$207.38	$207.40	$207.40
Purchase #3	$96.42	6.389%	$102.5803	$102.58	$102.60	$102.60
Purchase #4	$174.85	4.620%	$182.9281	$182.93	$182.95	$182.90
Purchase #5	$65.31	5.763%	$69.0738	$69.07	$69.05	$69.10
Purchase #6	$72.50	8.816%	$78.8916	$78.89	$78.90	$78.90
Purchase #7	$146.59	7.713%	$157.8965	$157.90	$157.90	$157.90
7 purchase totals =	$785.09		$841.5225	$841.52	$841.55	$841.60