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	$35.98	12.296%	$40.4041	$40.40	$40.40	$40.40
Purchase #2	$166.35	10.298%	$183.4807	$183.48	$183.50	$183.50
Purchase #3	$51.78	12.698%	$58.355	$58.36	$58.35	$58.40
Purchase #4	$126.61	3.758%	$131.368	$131.37	$131.35	$131.40
Purchase #5	$125.85	3.433%	$130.1704	$130.17	$130.15	$130.20
Purchase #6	$20.43	11.724%	$22.8252	$22.83	$22.85	$22.80
Purchase #7	$76.59	7.199%	$82.1037	$82.10	$82.10	$82.10
7 purchase totals =	$603.59		$648.7071	$648.71	$648.70	$648.80