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	$42.99	7.405%	$46.1734	$46.17	$46.15	$46.20
Purchase #2	$35.81	10.744%	$39.6574	$39.66	$39.65	$39.70
Purchase #3	$98.33	5.430%	$103.6693	$103.67	$103.65	$103.70
Purchase #4	$179.89	11.309%	$200.2338	$200.23	$200.25	$200.20
Purchase #5	$182.25	7.698%	$196.2796	$196.28	$196.30	$196.30
Purchase #6	$7.71	4.819%	$8.0815	$8.08	$8.10	$8.10
Purchase #7	$20.90	11.527%	$23.3091	$23.31	$23.30	$23.30
7 purchase totals =	$567.88		$617.4041	$617.40	$617.40	$617.50