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	$60.25	4.359%	$62.8763	$62.88	$62.90	$62.90
Purchase #2	$115.80	3.640%	$120.0151	$120.02	$120.00	$120.00
Purchase #3	$189.61	8.382%	$205.5031	$205.50	$205.50	$205.50
Purchase #4	$72.32	9.296%	$79.0429	$79.04	$79.05	$79.00
Purchase #5	$132.82	7.418%	$142.6726	$142.67	$142.65	$142.70
Purchase #6	$99.41	12.221%	$111.5589	$111.56	$111.55	$111.60
Purchase #7	$34.59	12.799%	$39.0172	$39.02	$39.00	$39.00
7 purchase totals =	$704.80		$760.6861	$760.69	$760.65	$760.70