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	$119.81	9.690%	$131.4196	$131.42	$131.40	$131.40
Purchase #2	$36.47	9.562%	$39.9573	$39.96	$39.95	$40.00
Purchase #3	$160.69	3.354%	$166.0795	$166.08	$166.10	$166.10
Purchase #4	$119.95	9.543%	$131.3968	$131.40	$131.40	$131.40
Purchase #5	$236.36	3.443%	$244.4979	$244.50	$244.50	$244.50
Purchase #6	$142.54	5.726%	$150.7018	$150.70	$150.70	$150.70
Purchase #7	$211.35	6.866%	$225.8613	$225.86	$225.85	$225.90
7 purchase totals =	$1,027.17		$1,089.9142	$1,089.92	$1,089.90	$1,090.00