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	$219.95	13.304%	$249.2121	$249.21	$249.20	$249.20
Purchase #2	$131.89	10.630%	$145.9099	$145.91	$145.90	$145.90
Purchase #3	$185.41	5.854%	$196.2639	$196.26	$196.25	$196.30
Purchase #4	$50.52	7.729%	$54.4247	$54.42	$54.40	$54.40
Purchase #5	$153.40	7.762%	$165.3069	$165.31	$165.30	$165.30
Purchase #6	$50.43	3.749%	$52.3206	$52.32	$52.30	$52.30
Purchase #7	$221.81	3.665%	$229.9393	$229.94	$229.95	$229.90
7 purchase totals =	$1,013.41		$1,093.3774	$1,093.37	$1,093.30	$1,093.30