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	$105.63	6.283%	$112.2667	$112.27	$112.25	$112.30
Purchase #2	$35.98	3.745%	$37.3275	$37.33	$37.35	$37.30
Purchase #3	$159.64	8.553%	$173.294	$173.29	$173.30	$173.30
Purchase #4	$206.56	9.373%	$225.9209	$225.92	$225.90	$225.90
Purchase #5	$111.41	11.684%	$124.4271	$124.43	$124.45	$124.40
Purchase #6	$150.65	10.352%	$166.2453	$166.25	$166.25	$166.20
Purchase #7	$28.44	8.586%	$30.8819	$30.88	$30.90	$30.90
7 purchase totals =	$798.31		$870.3634	$870.37	$870.40	$870.30