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	$39.96	12.302%	$44.8759	$44.88	$44.90	$44.90
Purchase #2	$134.62	6.465%	$143.3232	$143.32	$143.30	$143.30
Purchase #3	$58.76	9.444%	$64.3093	$64.31	$64.30	$64.30
Purchase #4	$41.97	12.150%	$47.0694	$47.07	$47.05	$47.10
Purchase #5	$6.64	6.735%	$7.0872	$7.09	$7.10	$7.10
Purchase #6	$93.51	6.501%	$99.5891	$99.59	$99.60	$99.60
Purchase #7	$187.78	4.780%	$196.7559	$196.76	$196.75	$196.80
7 purchase totals =	$563.24		$603.0100	$603.02	$603.00	$603.10