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	$18.57	8.418%	$20.1332	$20.13	$20.15	$20.10
Purchase #2	$187.27	12.736%	$211.1207	$211.12	$211.10	$211.10
Purchase #3	$124.74	11.819%	$139.483	$139.48	$139.50	$139.50
Purchase #4	$20.62	5.499%	$21.7539	$21.75	$21.75	$21.80
Purchase #5	$199.89	4.857%	$209.5987	$209.60	$209.60	$209.60
Purchase #6	$73.63	3.308%	$76.0657	$76.07	$76.05	$76.10
Purchase #7	$87.64	13.583%	$99.5441	$99.54	$99.55	$99.50
7 purchase totals =	$712.36		$777.6993	$777.69	$777.70	$777.70