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	$91.78	13.726%	$104.3777	$104.38	$104.40	$104.40
Purchase #2	$168.92	3.328%	$174.5417	$174.54	$174.55	$174.50
Purchase #3	$156.32	12.845%	$176.3993	$176.40	$176.40	$176.40
Purchase #4	$44.73	13.314%	$50.6854	$50.69	$50.70	$50.70
Purchase #5	$239.72	10.550%	$265.0105	$265.01	$265.00	$265.00
Purchase #6	$13.54	3.795%	$14.0538	$14.05	$14.05	$14.10
Purchase #7	$82.38	9.299%	$90.0405	$90.04	$90.05	$90.00
7 purchase totals =	$797.39		$875.1089	$875.11	$875.15	$875.10