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	$5.73	13.275%	$6.4907	$6.49	$6.50	$6.50
Purchase #2	$41.36	13.713%	$47.0317	$47.03	$47.05	$47.00
Purchase #3	$119.55	10.211%	$131.7573	$131.76	$131.75	$131.80
Purchase #4	$124.48	3.109%	$128.3501	$128.35	$128.35	$128.40
Purchase #5	$33.73	9.705%	$37.0035	$37.00	$37.00	$37.00
Purchase #6	$151.67	6.109%	$160.9355	$160.94	$160.95	$160.90
Purchase #7	$59.46	4.564%	$62.1738	$62.17	$62.15	$62.20
7 purchase totals =	$535.98		$573.7426	$573.74	$573.75	$573.80