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	$109.48	9.650%	$120.0448	$120.04	$120.05	$120.00
Purchase #2	$89.52	13.183%	$101.3214	$101.32	$101.30	$101.30
Purchase #3	$171.70	9.463%	$187.948	$187.95	$187.95	$187.90
Purchase #4	$83.64	8.150%	$90.4567	$90.46	$90.45	$90.50
Purchase #5	$146.86	7.785%	$158.2931	$158.29	$158.30	$158.30
Purchase #6	$152.53	6.570%	$162.5512	$162.55	$162.55	$162.60
Purchase #7	$98.89	3.740%	$102.5885	$102.59	$102.60	$102.60
7 purchase totals =	$852.62		$923.2037	$923.20	$923.20	$923.20