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	$144.42	13.619%	$164.0886	$164.09	$164.10	$164.10
Purchase #2	$20.25	7.284%	$21.725	$21.73	$21.75	$21.70
Purchase #3	$195.66	6.317%	$208.0198	$208.02	$208.00	$208.00
Purchase #4	$88.95	11.396%	$99.0867	$99.09	$99.10	$99.10
Purchase #5	$160.48	9.275%	$175.3645	$175.36	$175.35	$175.40
Purchase #6	$102.90	6.839%	$109.9373	$109.94	$109.95	$109.90
Purchase #7	$5.74	10.323%	$6.3325	$6.33	$6.35	$6.30
7 purchase totals =	$718.40		$784.5544	$784.56	$784.60	$784.50