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	$249.36	3.840%	$258.9354	$258.94	$258.95	$258.90
Purchase #2	$39.32	7.470%	$42.2572	$42.26	$42.25	$42.30
Purchase #3	$148.39	3.597%	$153.7276	$153.73	$153.75	$153.70
Purchase #4	$165.61	12.419%	$186.1771	$186.18	$186.20	$186.20
Purchase #5	$89.38	6.552%	$95.2362	$95.24	$95.25	$95.20
Purchase #6	$49.26	11.165%	$54.7599	$54.76	$54.75	$54.80
Purchase #7	$28.78	8.798%	$31.3121	$31.31	$31.30	$31.30
7 purchase totals =	$770.10		$822.4055	$822.42	$822.45	$822.40