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	$53.57	10.836%	$59.3748	$59.37	$59.35	$59.40
Purchase #2	$54.71	7.708%	$58.927	$58.93	$58.95	$58.90
Purchase #3	$119.86	5.847%	$126.8682	$126.87	$126.85	$126.90
Purchase #4	$98.26	5.222%	$103.3911	$103.39	$103.40	$103.40
Purchase #5	$78.76	13.364%	$89.2855	$89.29	$89.30	$89.30
Purchase #6	$38.79	5.566%	$40.9491	$40.95	$40.95	$40.90
Purchase #7	$68.59	6.752%	$73.2212	$73.22	$73.20	$73.20
7 purchase totals =	$512.54		$552.0169	$552.02	$552.00	$552.00