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	$38.26	9.752%	$41.9911	$41.99	$42.00	$42.00
Purchase #2	$37.31	6.205%	$39.6251	$39.63	$39.65	$39.60
Purchase #3	$37.86	13.300%	$42.8954	$42.90	$42.90	$42.90
Purchase #4	$181.37	9.474%	$198.553	$198.55	$198.55	$198.60
Purchase #5	$71.87	12.759%	$81.0399	$81.04	$81.05	$81.00
Purchase #6	$43.42	3.655%	$45.007	$45.01	$45.00	$45.00
Purchase #7	$34.56	13.704%	$39.2961	$39.30	$39.30	$39.30
7 purchase totals =	$444.65		$488.4076	$488.42	$488.45	$488.40