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	$239.31	13.168%	$270.8223	$270.82	$270.80	$270.80
Purchase #2	$6.71	7.530%	$7.2153	$7.22	$7.20	$7.20
Purchase #3	$45.31	5.682%	$47.8845	$47.88	$47.90	$47.90
Purchase #4	$130.29	5.238%	$137.1146	$137.11	$137.10	$137.10
Purchase #5	$147.75	11.533%	$164.79	$164.79	$164.80	$164.80
Purchase #6	$68.37	6.216%	$72.6199	$72.62	$72.60	$72.60
Purchase #7	$7.51	5.484%	$7.9218	$7.92	$7.90	$7.90
7 purchase totals =	$645.25		$708.3684	$708.36	$708.30	$708.30