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	$30.72	8.722%	$33.3994	$33.40	$33.40	$33.40
Purchase #2	$131.80	11.253%	$146.6315	$146.63	$146.65	$146.60
Purchase #3	$199.91	11.862%	$223.6233	$223.62	$223.60	$223.60
Purchase #4	$205.65	12.516%	$231.3892	$231.39	$231.40	$231.40
Purchase #5	$230.51	4.792%	$241.556	$241.56	$241.55	$241.60
Purchase #6	$218.34	3.171%	$225.2636	$225.26	$225.25	$225.30
Purchase #7	$232.27	11.309%	$258.5374	$258.54	$258.55	$258.50
7 purchase totals =	$1,249.20		$1,360.4004	$1,360.40	$1,360.40	$1,360.40