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	$77.84	6.376%	$82.8031	$82.80	$82.80	$82.80
Purchase #2	$65.28	7.152%	$69.9488	$69.95	$69.95	$69.90
Purchase #3	$164.63	6.265%	$174.9441	$174.94	$174.95	$174.90
Purchase #4	$97.86	7.617%	$105.314	$105.31	$105.30	$105.30
Purchase #5	$104.59	5.237%	$110.0674	$110.07	$110.05	$110.10
Purchase #6	$102.45	6.859%	$109.477	$109.48	$109.50	$109.50
Purchase #7	$150.64	7.761%	$162.3312	$162.33	$162.35	$162.30
7 purchase totals =	$763.29		$814.8856	$814.88	$814.90	$814.80